locking: Make rwsem_assert_held_write_nolockdep() build with PREEMPT_RT=y

The commit cited below broke the build for PREEMPT_RT because
rwsem_assert_held_write_nolockdep() passes a struct rw_semapho

locking: Make rwsem_assert_held_write_nolockdep() build with PREEMPT_RT=y

The commit cited below broke the build for PREEMPT_RT because
rwsem_assert_held_write_nolockdep() passes a struct rw_semaphore but
rw_base_assert_held_write() expects struct rwbase_rt. Fixing the type alone
leads to the problem that WARN_ON() is not found because bug.h is missing.

In order to resolve this:

- Keep the assert (WARN_ON()) in rwsem.h (not rwbase_rt.h)

- Make rwsem_assert_held_write_nolockdep() do the implementation
specific (rw_base) writer check.

- Replace the "inline" with __always_inline which was used before.

Fixes: f70405afc99b1 ("locking: Add rwsem_assert_held() and rwsem_assert_held_write()")
Reported-by: Clark Williams <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking: Add rwsem_assert_held() and rwsem_assert_held_write()

Modelled after lockdep_assert_held() and lockdep_assert_held_write(),
but are always active, even when lockdep is disabled. Of course,

locking: Add rwsem_assert_held() and rwsem_assert_held_write()

Modelled after lockdep_assert_held() and lockdep_assert_held_write(),
but are always active, even when lockdep is disabled. Of course, they
don't test that _this_ thread is the owner, but it's sufficient to catch
many bugs and doesn't incur the same performance penalty as lockdep.

Acked-by: "Peter Zijlstra (Intel)" <[email protected]>
Acked-by: Waiman Long <[email protected]>
Acked-by: "Darrick J. Wong" <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Signed-off-by: "Matthew Wilcox (Oracle)" <[email protected]>
Signed-off-by: Chandan Babu R <[email protected]>

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cleanup: Add conditional guard support

Adds:

- DEFINE_GUARD_COND() / DEFINE_LOCK_GUARD_1_COND() to extend existing
guards with conditional lock primitives, eg. mutex_trylock(),
mutex_lock_in

cleanup: Add conditional guard support

Adds:

- DEFINE_GUARD_COND() / DEFINE_LOCK_GUARD_1_COND() to extend existing
guards with conditional lock primitives, eg. mutex_trylock(),
mutex_lock_interruptible().

nb. both primitives allow NULL 'locks', which cause the lock to
fail (obviously).

- extends scoped_guard() to not take the body when the the
conditional guard 'fails'. eg.

scoped_guard (mutex_intr, &task->signal_cred_guard_mutex) {
...
}

will only execute the body when the mutex is held.

- provides scoped_cond_guard(name, fail, args...); which extends
scoped_guard() to do fail when the lock-acquire fails.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/20231102110706.460851167%40infradead.org

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locking: Introduce __cleanup() based infrastructure

Use __attribute__((__cleanup__(func))) to build:

- simple auto-release pointers using __free()

- 'classes' with constructor and destructor sem

locking: Introduce __cleanup() based infrastructure

Use __attribute__((__cleanup__(func))) to build:

- simple auto-release pointers using __free()

- 'classes' with constructor and destructor semantics for
scope-based resource management.

- lock guards based on the above classes.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/20230612093537.614161713%40infradead.org

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locking/rwsem: drop redundant semicolon of down_write_nest_lock

Otherwise, braces are needed when using it.

Signed-off-by: Guchun Chen <[email protected]>
Acked-by: Christian König <christian.koe

locking/rwsem: drop redundant semicolon of down_write_nest_lock

Otherwise, braces are needed when using it.

Signed-off-by: Guchun Chen <[email protected]>
Acked-by: Christian König <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Christian König <[email protected]>

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kernel.h: drop unneeded <linux/kernel.h> inclusion from other headers

Patch series "kernel.h further split", v5.

kernel.h is a set of something which is not related to each other and
often used in

kernel.h: drop unneeded <linux/kernel.h> inclusion from other headers

Patch series "kernel.h further split", v5.

kernel.h is a set of something which is not related to each other and
often used in non-crossed compilation units, especially when drivers
need only one or two macro definitions from it.

This patch (of 7):

There is no evidence we need kernel.h inclusion in certain headers.
Drop unneeded <linux/kernel.h> inclusion from other headers.

[[email protected]: bottom_half.h needs kernel]
Link: https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Andy Shevchenko <[email protected]>
Signed-off-by: Stephen Rothwell <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Brendan Higgins <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Sakari Ailus <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Thorsten Leemhuis <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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locking/rwsem: Add missing __init_rwsem() for PREEMPT_RT

730633f0b7f95 became the first direct caller of __init_rwsem() vs the
usual init_rwsem(), exposing PREEMPT_RT's lack thereof. Add it.

[ tgl

locking/rwsem: Add missing __init_rwsem() for PREEMPT_RT

730633f0b7f95 became the first direct caller of __init_rwsem() vs the
usual init_rwsem(), exposing PREEMPT_RT's lack thereof. Add it.

[ tglx: Move it out of line ]

Signed-off-by: Mike Galbraith <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking/rwsem: Add rtmutex based R/W semaphore implementation

The RT specific R/W semaphore implementation used to restrict the number of
readers to one, because a writer cannot block on multiple re

locking/rwsem: Add rtmutex based R/W semaphore implementation

The RT specific R/W semaphore implementation used to restrict the number of
readers to one, because a writer cannot block on multiple readers and
inherit its priority or budget.

The single reader restricting was painful in various ways:

- Performance bottleneck for multi-threaded applications in the page fault
path (mmap sem)

- Progress blocker for drivers which are carefully crafted to avoid the
potential reader/writer deadlock in mainline.

The analysis of the writer code paths shows that properly written RT tasks
should not take them. Syscalls like mmap(), file access which take mmap sem
write locked have unbound latencies, which are completely unrelated to mmap
sem. Other R/W sem users like graphics drivers are not suitable for RT tasks
either.

So there is little risk to hurt RT tasks when the RT rwsem implementation is
done in the following way:

- Allow concurrent readers

- Make writers block until the last reader left the critical section. This
blocking is not subject to priority/budget inheritance.

- Readers blocked on a writer inherit their priority/budget in the normal
way.

There is a drawback with this scheme: R/W semaphores become writer unfair
though the applications which have triggered writer starvation (mostly on
mmap_sem) in the past are not really the typical workloads running on a RT
system. So while it's unlikely to hit writer starvation, it's possible. If
there are unexpected workloads on RT systems triggering it, the problem
has to be revisited.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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locking: Fix typos in comments

Fix ~16 single-word typos in locking code comments.

Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Paul E. McKenney <paulmck@k

locking: Fix typos in comments

Fix ~16 single-word typos in locking code comments.

Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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rwsem: Implement down_read_interruptible

In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_interruptible. T

rwsem: Implement down_read_interruptible

In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_interruptible. This is needed for perf_event_open to be
converted (with no semantic changes) from working on a mutex to
wroking on a rwsem.

Signed-off-by: Eric W. Biederman <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

show more ...

rwsem: Implement down_read_killable_nested

In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_killable_nested

rwsem: Implement down_read_killable_nested

In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_killable_nested. This is needed so that kcmp_lock
can be converted from working on a mutexes to working on rw_semaphores.

Signed-off-by: Eric W. Biederman <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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rwsem: fix commas in initialisation

Leading comma prevents arbitrary reordering of initialisation clauses.
The whole point of C99 initialisation is to allow any such reordering.

Signed-off-by: Alex

rwsem: fix commas in initialisation

Leading comma prevents arbitrary reordering of initialisation clauses.
The whole point of C99 initialisation is to allow any such reordering.

Signed-off-by: Alexey Dobriyan <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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lockdep: Introduce wait-type checks

Extend lockdep to validate lock wait-type context.

The current wait-types are:

LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spi

lockdep: Introduce wait-type checks

Extend lockdep to validate lock wait-type context.

The current wait-types are:

LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spinlock_t etc.. */
LD_WAIT_CONFIG, /* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
LD_WAIT_SLEEP, /* sleeping locks, mutex_t etc.. */

Where lockdep validates that the current lock (the one being acquired)
fits in the current wait-context (as generated by the held stack).

This ensures that there is no attempt to acquire mutexes while holding
spinlocks, to acquire spinlocks while holding raw_spinlocks and so on. In
other words, its a more fancy might_sleep().

Obviously RCU made the entire ordeal more complex than a simple single
value test because RCU can be acquired in (pretty much) any context and
while it presents a context to nested locks it is not the same as it
got acquired in.

Therefore its necessary to split the wait_type into two values, one
representing the acquire (outer) and one representing the nested context
(inner). For most 'normal' locks these two are the same.

[ To make static initialization easier we have the rule that:
.outer == INV means .outer == .inner; because INV == 0. ]

It further means that its required to find the minimal .inner of the held
stack to compare against the outer of the new lock; because while 'normal'
RCU presents a CONFIG type to nested locks, if it is taken while already
holding a SPIN type it obviously doesn't relax the rules.

Below is an example output generated by the trivial test code:

raw_spin_lock(&foo);
spin_lock(&bar);
spin_unlock(&bar);
raw_spin_unlock(&foo);

[ BUG: Invalid wait context ]
-----------------------------
swapper/0/1 is trying to lock:
ffffc90000013f20 (&bar){....}-{3:3}, at: kernel_init+0xdb/0x187
other info that might help us debug this:
1 lock held by swapper/0/1:
#0: ffffc90000013ee0 (&foo){+.+.}-{2:2}, at: kernel_init+0xd1/0x187

The way to read it is to look at the new -{n,m} part in the lock
description; -{3:3} for the attempted lock, and try and match that up to
the held locks, which in this case is the one: -{2,2}.

This tells that the acquiring lock requires a more relaxed environment than
presented by the lock stack.

Currently only the normal locks and RCU are converted, the rest of the
lockdep users defaults to .inner = INV which is ignored. More conversions
can be done when desired.

The check for spinlock_t nesting is not enabled by default. It's a separate
config option for now as there are known problems which are currently
addressed. The config option allows to identify these problems and to
verify that the solutions found are indeed solving them.

The config switch will be removed and the checks will permanently enabled
once the vast majority of issues has been addressed.

[ bigeasy: Move LD_WAIT_FREE,… out of CONFIG_LOCKDEP to avoid compile
failure with CONFIG_DEBUG_SPINLOCK + !CONFIG_LOCKDEP]
[ tglx: Add the config option ]

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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locking/rwsem: Remove RWSEM_OWNER_UNKNOWN

Remove the now unused RWSEM_OWNER_UNKNOWN hack. This hack breaks
PREEMPT_RT and getting rid of it was the entire motivation for
re-writing the percpu rwsem.

locking/rwsem: Remove RWSEM_OWNER_UNKNOWN

Remove the now unused RWSEM_OWNER_UNKNOWN hack. This hack breaks
PREEMPT_RT and getting rid of it was the entire motivation for
re-writing the percpu rwsem.

The biggest problem is that it is fundamentally incompatible with any
form of Priority Inheritance, any exclusively held lock must have a
distinct owner.

Requested-by: Christoph Hellwig <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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locking/rwsem: Check for operations on an uninitialized rwsem

Currently rwsems is the only locking primitive that lacks this
debug feature. Add it under CONFIG_DEBUG_RWSEMS and do the magic
checking

locking/rwsem: Check for operations on an uninitialized rwsem

Currently rwsems is the only locking primitive that lacks this
debug feature. Add it under CONFIG_DEBUG_RWSEMS and do the magic
checking in the locking fastpath (trylock) operation such that
we cover all cases. The unlocking part is pretty straightforward.

Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Waiman Long <[email protected]>
Cc: [email protected]
Cc: Davidlohr Bueso <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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docs: locking: convert docs to ReST and rename to *.rst

Convert the locking documents to ReST and add them to the
kernel development book where it belongs.

Most of the stuff here is just to make Sp

docs: locking: convert docs to ReST and rename to *.rst

Convert the locking documents to ReST and add them to the
kernel development book where it belongs.

Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.

The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <[email protected]>
Acked-by: Federico Vaga <[email protected]>

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locking/rwsem: Make rwsem->owner an atomic_long_t

The rwsem->owner contains not just the task structure pointer, it also
holds some flags for storing the current state of the rwsem. Some of
the flag

locking/rwsem: Make rwsem->owner an atomic_long_t

The rwsem->owner contains not just the task structure pointer, it also
holds some flags for storing the current state of the rwsem. Some of
the flags may have to be atomically updated. To reflect the new reality,
the owner is now changed to an atomic_long_t type.

New helper functions are added to properly separate out the task
structure pointer and the embedded flags.

Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: huang ying <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/rwsem: Clarify usage of owner's nonspinaable bit

Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an
anonymous owner - readers or an anonymous writer. The setting of this
a

locking/rwsem: Clarify usage of owner's nonspinaable bit

Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an
anonymous owner - readers or an anonymous writer. The setting of this
anonymous bit is used as an indicator that optimistic spinning cannot
be done on this rwsem.

With the upcoming reader optimistic spinning patches, a reader-owned
rwsem can be spinned on for a limit period of time. We still need
this bit to indicate a rwsem is nonspinnable, but not setting this
bit loses its meaning that the owner is known. So rename the bit
to RWSEM_NONSPINNABLE to clarify its meaning.

This patch also fixes a DEBUG_RWSEMS_WARN_ON() bug in __up_write().

Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: huang ying <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER

The owner field in the rw_semaphore structure is used primarily for
optimistic spinning. However, identifying the rwsem owner

locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER

The owner field in the rw_semaphore structure is used primarily for
optimistic spinning. However, identifying the rwsem owner can also be
helpful in debugging as well as tracing locking related issues when
analyzing crash dump. The owner field may also store state information
that can be important to the operation of the rwsem.

So the owner field is now made a permanent member of the rw_semaphore
structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER.

Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: huang ying <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/rwsem: Optimize rwsem structure for uncontended lock acquisition

For an uncontended rwsem, count and owner are the only fields a task
needs to touch when acquiring the rwsem. So they are put

locking/rwsem: Optimize rwsem structure for uncontended lock acquisition

For an uncontended rwsem, count and owner are the only fields a task
needs to touch when acquiring the rwsem. So they are put next to each
other to increase the chance that they will share the same cacheline.

On a ThunderX2 99xx (arm64) system with 32K L1 cache and 256K L2
cache, a rwsem locking microbenchmark with one locking thread was
run to write-lock and write-unlock an array of rwsems separated 2
cachelines apart in a 1M byte memory block. The locking rates (kops/s)
of the microbenchmark when the rwsems are at various "long" (8-byte)
offsets from beginning of the cacheline before and after the patch were
as follows:

Cacheline Offset Pre-patch Post-patch
---------------- --------- ----------
0 17,449 16,588
1 17,450 16,465
2 17,450 16,460
3 17,453 16,462
4 14,867 16,471
5 14,867 16,470
6 14,853 16,464
7 14,867 13,172

Before the patch, the count and owner are 4 "long"s apart. After the
patch, they are only 1 "long" apart.

The rwsem data have to be loaded from the L3 cache for each access. It
can be seen that the locking rates are more consistent after the patch
than before. Note that for this particular system, the performance
drop happens whenever the count and owner are at an odd multiples of
"long"s apart. No performance drop was observed when only a single rwsem
was used (hot cache). So the drop is likely just an idiosyncrasy of the
cache architecture of this chip than an inherent problem with the patch.

Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Will Deacon <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

locking/rwsem: Move rwsem internal function declarations to rwsem-xadd.h

We don't need to expose rwsem internal functions which are not supposed
to be called directly from other kernel code.

Signed

locking/rwsem: Move rwsem internal function declarations to rwsem-xadd.h

We don't need to expose rwsem internal functions which are not supposed
to be called directly from other kernel code.

Signed-off-by: Waiman Long <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all archs

Currently, we have two different implementation of rwsem:

1) CONFIG_RWSEM_GENERIC_SPINLOCK (rwsem-spinlock.c)
2) CONFIG_RWS

locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all archs

Currently, we have two different implementation of rwsem:

1) CONFIG_RWSEM_GENERIC_SPINLOCK (rwsem-spinlock.c)
2) CONFIG_RWSEM_XCHGADD_ALGORITHM (rwsem-xadd.c)

As we are going to use a single generic implementation for rwsem-xadd.c
and no architecture-specific code will be needed, there is no point
in keeping two different implementations of rwsem. In most cases, the
performance of rwsem-spinlock.c will be worse. It also doesn't get all
the performance tuning and optimizations that had been implemented in
rwsem-xadd.c over the years.

For simplication, we are going to remove rwsem-spinlock.c and make all
architectures use a single implementation of rwsem - rwsem-xadd.c.

All references to RWSEM_GENERIC_SPINLOCK and RWSEM_XCHGADD_ALGORITHM
in the code are removed.

Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/rwsem: Remove arch specific rwsem files

As the generic rwsem-xadd code is using the appropriate acquire and
release versions of the atomic operations, the arch specific rwsem.h
files will no

locking/rwsem: Remove arch specific rwsem files

As the generic rwsem-xadd code is using the appropriate acquire and
release versions of the atomic operations, the arch specific rwsem.h
files will not be that much faster than the generic code as long as the
atomic functions are properly implemented. So we can remove those arch
specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
effort.

Currently, only x86, alpha and ia64 have implemented architecture
specific fast paths. I don't have access to alpha and ia64 systems for
testing, but they are legacy systems that are not likely to be updated
to the latest kernel anyway.

By using a rwsem microbenchmark, the total locking rates on a 4-socket
56-core 112-thread x86-64 system before and after the patch were as
follows (mixed means equal # of read and write locks):

Before Patch After Patch
# of Threads wlock rlock mixed wlock rlock mixed
------------ ----- ----- ----- ----- ----- -----
1 29,201 30,143 29,458 28,615 30,172 29,201
2 6,807 13,299 1,171 7,725 15,025 1,804
4 6,504 12,755 1,520 7,127 14,286 1,345
8 6,762 13,412 764 6,826 13,652 726
16 6,693 15,408 662 6,599 15,938 626
32 6,145 15,286 496 5,549 15,487 511
64 5,812 15,495 60 5,858 15,572 60

There were some run-to-run variations for the multi-thread tests. For
x86-64, using the generic C code fast path seems to be a little bit
faster than the assembly version with low lock contention. Looking at
the assembly version of the fast paths, there are assembly to/from C
code wrappers that save and restore all the callee-clobbered registers
(7 registers on x86-64). The assembly generated from the generic C
code doesn't need to do that. That may explain the slight performance
gain here.

The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
with no code change as no other code other than those under
kernel/locking needs to access the internal rwsem macros and functions.

Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/rwsem: Make owner store task pointer of last owning reader

Currently, when a reader acquires a lock, it only sets the
RWSEM_READER_OWNED bit in the owner field. The other bits are simply
not

locking/rwsem: Make owner store task pointer of last owning reader

Currently, when a reader acquires a lock, it only sets the
RWSEM_READER_OWNED bit in the owner field. The other bits are simply
not used. When debugging hanging cases involving rwsems and readers,
the owner value does not provide much useful information at all.

This patch modifies the current behavior to always store the task_struct
pointer of the last rwsem-acquiring reader in a reader-owned rwsem. This
may be useful in debugging rwsem hanging cases especially if only one
reader is involved. However, the task in the owner field may not the
real owner or one of the real owners at all when the owner value is
examined, for example, in a crash dump. So it is just an additional
hint about the past history.

If CONFIG_DEBUG_RWSEMS=y is enabled, the owner field will be checked at
unlock time too to make sure the task pointer value is valid. That does
have a slight performance cost and so is only enabled as part of that
debug option.

From the performance point of view, it is expected that the changes
shouldn't have any noticeable performance impact. A rwsem microbenchmark
(with 48 worker threads and 1:1 reader/writer ratio) was ran on a
2-socket 24-core 48-thread Haswell system. The locking rates on a
4.19-rc1 based kernel were as follows:

1) Unpatched kernel: 543.3 kops/s
2) Patched kernel: 549.2 kops/s
3) Patched kernel (CONFIG_DEBUG_RWSEMS on): 546.6 kops/s

There was actually a slight increase in performance (1.1%) in this
particular case. Maybe it was caused by the elimination of a branch or
just a testing noise. Turning on the CONFIG_DEBUG_RWSEMS option also
had less than the expected impact on performance.

The least significant 2 bits of the owner value are now used to designate
the rwsem is readers owned and the owners are anonymous.

Signed-off-by: Waiman Long <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN

The filesystem freezing code needs to transfer ownership of a rwsem
embedded in a percpu-rwsem from the task th

locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN

The filesystem freezing code needs to transfer ownership of a rwsem
embedded in a percpu-rwsem from the task that does the freezing to
another one that does the thawing by calling percpu_rwsem_release()
after freezing and percpu_rwsem_acquire() before thawing.

However, the new rwsem debug code runs afoul with this scheme by warning
that the task that releases the rwsem isn't the one that acquires it,
as reported by Amir Goldstein:

DEBUG_LOCKS_WARN_ON(sem->owner != get_current())
WARNING: CPU: 1 PID: 1401 at /home/amir/build/src/linux/kernel/locking/rwsem.c:133 up_write+0x59/0x79

Call Trace:
percpu_up_write+0x1f/0x28
thaw_super_locked+0xdf/0x120
do_vfs_ioctl+0x270/0x5f1
ksys_ioctl+0x52/0x71
__x64_sys_ioctl+0x16/0x19
do_syscall_64+0x5d/0x167
entry_SYSCALL_64_after_hwframe+0x49/0xbe

To work properly with the rwsem debug code, we need to annotate that the
rwsem ownership is unknown during the tranfer period until a brave soul
comes forward to acquire the ownership. During that period, optimistic
spinning will be disabled.

Reported-by: Amir Goldstein <[email protected]>
Tested-by: Amir Goldstein <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Theodore Y. Ts'o <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...