kref: Improve documentation

There is already kernel-doc written for many of the functions in kref.h
but it's not linked into the html docs anywhere. Add it to kref.rst.

Improve the kref documentat

kref: Improve documentation

There is already kernel-doc written for many of the functions in kref.h
but it's not linked into the html docs anywhere. Add it to kref.rst.

Improve the kref documentation by using the standard Return: section,
rewording some unclear verbiage and adding docs for some undocumented
functions.

Update Thomas' email address to his current one.

Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Tested-by: Randy Dunlap <[email protected]>
Acked-by: Randy Dunlap <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 428

Based on 1 normalized pattern(s):

this file is released under the gplv2

extracted by the scancode license scanner the SPDX lice

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 428

Based on 1 normalized pattern(s):

this file is released under the gplv2

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 68 file(s).

Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Armijn Hemel <[email protected]>
Reviewed-by: Allison Randal <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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kref/kobject: Improve documentation

The current kref and kobject documentation may be
insufficient to understand these common pitfalls regarding
object lifetime and object releasing.

Add a bit more

kref/kobject: Improve documentation

The current kref and kobject documentation may be
insufficient to understand these common pitfalls regarding
object lifetime and object releasing.

Add a bit more documentation and improve the warnings
seen by the user, pointing to the right piece of documentation.

Also, it's important to understand that making fun of people
publicly is not at all helpful, doesn't provide any value,
and it's not a healthy way of encouraging developers to do better.

"Mocking mercilessly" will, if anything, make developers feel bad
and go away. This kind of behavior should not be encouraged or justified.

Signed-off-by: Ezequiel Garcia <[email protected]>
Signed-off-by: Enric Balletbo i Serra <[email protected]>
Signed-off-by: Gustavo Padovan <[email protected]>
Signed-off-by: Matthias Brugger <[email protected]>
Acked-by: Daniel Vetter <[email protected]>
Acked-by: Guenter Roeck <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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kref: remove WARN_ON for NULL release functions

The kref functions check for NULL release functions. This WARN_ON seems
rather pointless. We will eventually release and then just crash
nicely. It

kref: remove WARN_ON for NULL release functions

The kref functions check for NULL release functions. This WARN_ON seems
rather pointless. We will eventually release and then just crash
nicely. It is also somewhat expensive because these functions are
inlined in a lot of places. Removing the WARN_ONs saves around 2.3k in
this kernel (likely more in others with more drivers)

text data bss dec hex filename
9083992 5367600 11116544 25568136 1862388 vmlinux-before-load-avg
9070166 5367600 11116544 25554310 185ed86 vmlinux-load-avg

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Andi Kleen <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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kref: Implement 'struct kref' using refcount_t

Use the refcount_t 'atomic' type to implement 'struct kref', this makes kref
more robust by bringing saturation semantics.

Signed-off-by: Peter Zijlst

kref: Implement 'struct kref' using refcount_t

Use the refcount_t 'atomic' type to implement 'struct kref', this makes kref
more robust by bringing saturation semantics.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

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locking/atomic, kref: Implement kref_put_lock()

Because home-rolling your own is _awesome_, stop doing it. Provide
kref_put_lock(), just like kref_put_mutex() but for a spinlock.

Signed-off-by: Pet

locking/atomic, kref: Implement kref_put_lock()

Because home-rolling your own is _awesome_, stop doing it. Provide
kref_put_lock(), just like kref_put_mutex() but for a spinlock.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/atomic, kref: Kill kref_sub()

By general sentiment kref_sub() is a bad interface, make it go away.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <akpm@linux

locking/atomic, kref: Kill kref_sub()

By general sentiment kref_sub() is a bad interface, make it go away.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/atomic, kref: Add kref_read()

Since we need to change the implementation, stop exposing internals.

Provide kref_read() to read the current reference count; typically
used for debug messages

locking/atomic, kref: Add kref_read()

Since we need to change the implementation, stop exposing internals.

Provide kref_read() to read the current reference count; typically
used for debug messages.

Kills two anti-patterns:

atomic_read(&kref->refcount)
kref->refcount.counter

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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locking/atomic, kref: Add KREF_INIT()

Since we need to change the implementation, stop exposing internals.

Provide KREF_INIT() to allow static initialization of struct kref.

Signed-off-by: Peter Z

locking/atomic, kref: Add KREF_INIT()

Since we need to change the implementation, stop exposing internals.

Provide KREF_INIT() to allow static initialization of struct kref.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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kref: prefer atomic_inc_not_zero to atomic_add_unless

On most platforms, there exists this ifdef:

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)

This makes this patch functionally us

kref: prefer atomic_inc_not_zero to atomic_add_unless

On most platforms, there exists this ifdef:

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)

This makes this patch functionally useless. However, on PPC, there is
actually an explicit definition of atomic_inc_not_zero with its own
assembly that is slightly more optimized than atomic_add_unless. So,
this patch changes kref to use atomic_inc_not_zero instead, for PPC and
any future platforms that might provide an explicit implementation.

This also puts this usage of kref more in line with a verbatim reading
of the examples in Paul McKenney's paper [1] in the section titled "2.4
Atomic Counting With Check and Release Memory Barrier", which uses
atomic_inc_not_zero.

[1] http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2167.pdf

Signed-off-by: Jason A. Donenfeld <[email protected]>
Reviewed-by: Thomas Hellstrom <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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kref: prefer atomic_inc_not_zero to atomic_add_unless

On most platforms, there exists this ifdef:

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)

This makes this patch functionally us

kref: prefer atomic_inc_not_zero to atomic_add_unless

On most platforms, there exists this ifdef:

#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)

This makes this patch functionally useless. However, on PPC, there is
actually an explicit definition of atomic_inc_not_zero with its own
assembly that is slightly more optimized than atomic_add_unless. So,
this patch changes kref to use atomic_inc_not_zero instead, for PPC and
any future platforms that might provide an explicit implementation.

This also puts this usage of kref more in line with a verbatim reading
of the examples in Paul McKenney's paper [1] in the section titled "2.4
Atomic Counting With Check and Release Memory Barrier", which uses
atomic_inc_not_zero.

[1] http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2167.pdf

Signed-off-by: Jason A. Donenfeld <[email protected]>
Reviewed-by: Thomas Hellstrom <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]

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kref: Remove kref_put_spinlock_irqsave()

The last user is gone. Hence remove this function.

Signed-off-by: Bart Van Assche <[email protected]>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundatio

kref: Remove kref_put_spinlock_irqsave()

The last user is gone. Hence remove this function.

Signed-off-by: Bart Van Assche <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Joern Engel <[email protected]>
Signed-off-by: Nicholas Bellinger <[email protected]>

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target: close target_put_sess_cmd() vs. core_tmr_abort_task() race

It is possible for one thread to to take se_sess->sess_cmd_lock in
core_tmr_abort_task() before taking a reference count on
se_cmd-

target: close target_put_sess_cmd() vs. core_tmr_abort_task() race

It is possible for one thread to to take se_sess->sess_cmd_lock in
core_tmr_abort_task() before taking a reference count on
se_cmd->cmd_kref, while another thread in target_put_sess_cmd() drops
se_cmd->cmd_kref before taking se_sess->sess_cmd_lock.

This introduces kref_put_spinlock_irqsave() and uses it in
target_put_sess_cmd() to close the race window.

Signed-off-by: Joern Engel <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Cc: <[email protected]>
Signed-off-by: Nicholas Bellinger <[email protected]>

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kref: minor cleanup

- make warning smp-safe
- result of atomic _unless_zero functions should be checked by caller
to avoid use-after-free error
- trivial whitespace fix.

Link: https://lkml.or

kref: minor cleanup

- make warning smp-safe
- result of atomic _unless_zero functions should be checked by caller
to avoid use-after-free error
- trivial whitespace fix.

Link: https://lkml.org/lkml/2013/4/12/391

Tested: compile x86, boot machine and run xfstests
Signed-off-by: Anatol Pomozov <[email protected]>
[ Removed line-break, changed to use WARN_ON_ONCE() - Linus ]
Signed-off-by: Linus Torvalds <[email protected]>

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kref: Implement kref_get_unless_zero v3

This function is intended to simplify locking around refcounting for
objects that can be looked up from a lookup structure, and which are
removed from that lo

kref: Implement kref_get_unless_zero v3

This function is intended to simplify locking around refcounting for
objects that can be looked up from a lookup structure, and which are
removed from that lookup structure in the object destructor.
Operations on such objects require at least a read lock around
lookup + kref_get, and a write lock around kref_put + remove from lookup
structure. Furthermore, RCU implementations become extremely tricky.
With a lookup followed by a kref_get_unless_zero *with return value check*
locking in the kref_put path can be deferred to the actual removal from
the lookup structure and RCU lookups become trivial.

v2: Formatting fixes.
v3: Invert the return value.

Signed-off-by: Thomas Hellstrom <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>

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introduce kref_put_mutex()

equivalent of
mutex_lock(mutex);
if (!kref_put(kref, release))
mutex_unlock(mutex);

Signed-off-by: Al Viro <[email protected]>

Fix compile breakage with kref.h

This set of build failures just started appearing on parisc:

In file included from drivers/input/serio/serio_raw.c:12:
include/linux/kref.h: In function 'kref_g

Fix compile breakage with kref.h

This set of build failures just started appearing on parisc:

In file included from drivers/input/serio/serio_raw.c:12:
include/linux/kref.h: In function 'kref_get':
include/linux/kref.h:40: error: 'TAINT_WARN' undeclared (first use in this function)
include/linux/kref.h:40: error: (Each undeclared identifier is reported only once
include/linux/kref.h:40: error: for each function it appears in.)
include/linux/kref.h: In function 'kref_sub':
include/linux/kref.h:65: error: 'TAINT_WARN' undeclared (first use in this function)

It happens because TAINT_WARN is defined in kernel.h and this particular
compile doesn't seem to include it (no idea why it's just manifesting ..
probably some #include file untangling exposed it).

Fix by adding

#include <linux/kernel.h>

to linux/kref.h

Signed-off-by: James Bottomley <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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kref: fix up the kfree build problems

It turns out that some memory allocators use kobjects, which use krefs,
and kref.h was wanting to figure out the address of kfree(), which ended
up in a loop.

kref: fix up the kfree build problems

It turns out that some memory allocators use kobjects, which use krefs,
and kref.h was wanting to figure out the address of kfree(), which ended
up in a loop.

kfree was only being needed for a warning to tell the caller that they
were doing something stupid. Now we just move that warning into the
comments for the functions, which results in a bit more fun as everyone
enjoys digging for people to mock at times of boredom.

So, remove the dependancy of slab.h on kref.h, and fix up the other
include file as well (we really only need bug.h and atomic.h, not
types.h).

Reported-by: Stephen Rothwell <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Oliver Neukum <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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kref: Remove the memory barriers

Commit 1b0b3b9980e ("kref: fix CPU ordering with respect to krefs")
wrongly adds memory barriers to kref.

It states:

some atomic operations are only atomic, not

kref: Remove the memory barriers

Commit 1b0b3b9980e ("kref: fix CPU ordering with respect to krefs")
wrongly adds memory barriers to kref.

It states:

some atomic operations are only atomic, not ordered. Thus a CPU is allowed
to reorder memory references to an object to before the reference is
obtained. This fixes it.

While true, it fails to show why this is a problem. I say it is not a
problem because if there is a race with kref_put() such that we could
end up referencing a free'd object without this memory barrier, we
would still have that race with the memory barrier.

The kref_put() in question could complete (and free the object) before
the atomic_inc() and we'd still be up shit creek.

The kref_init() case is even worse, if your object is published at this
time you're so wrong the memory barrier won't make a difference what
so ever. If its not published, the act of publishing should include
the needed barriers/locks to make sure all writes prior to the act of
publishing are complete such that others will only observe a complete
object.

Cc: Alexey Dobriyan <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Oliver Neukum <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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kref: Implement kref_put in terms of kref_sub

Less lines of code is better.

Cc: Alexey Dobriyan <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signe

kref: Implement kref_put in terms of kref_sub

Less lines of code is better.

Cc: Alexey Dobriyan <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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kref: Inline all functions

These are tiny functions, there's no point in having them out-of-line.

Cc: Alexey Dobriyan <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar

kref: Inline all functions

These are tiny functions, there's no point in having them out-of-line.

Cc: Alexey Dobriyan <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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block: add internal hd part table references

We can't use krefs since it's apparently restricted to very basic
reference counting.

This reverts commit e4a683c8.

Signed-off-by: Jens Axboe <jaxboe@f

block: add internal hd part table references

We can't use krefs since it's apparently restricted to very basic
reference counting.

This reverts commit e4a683c8.

Signed-off-by: Jens Axboe <[email protected]>

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kref: add kref_test_and_get

Add kref_test_and_get() function, which atomically add a reference only if
refcount is not zero. This prevent to add a reference to an object that is
already being remove

kref: add kref_test_and_get

Add kref_test_and_get() function, which atomically add a reference only if
refcount is not zero. This prevent to add a reference to an object that is
already being removed.

Signed-off-by: Jerome Marchand <[email protected]>
Cc: [email protected]
Signed-off-by: Jens Axboe <[email protected]>

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kref: Add a kref_sub function

Makes it possible to optimize batched multiple unrefs.
Initial user will be drivers/gpu/ttm which accumulates unrefs to be
processed outside of atomic code.

Signed-off

kref: Add a kref_sub function

Makes it possible to optimize batched multiple unrefs.
Initial user will be drivers/gpu/ttm which accumulates unrefs to be
processed outside of atomic code.

Signed-off-by: Thomas Hellstrom <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>

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kref: remove kref_set

Of the three uses of kref_set in the kernel:

One really should be kref_put as the code is letting go of a
reference,
Two really should be kref_init because the kref is b

kref: remove kref_set

Of the three uses of kref_set in the kernel:

One really should be kref_put as the code is letting go of a
reference,
Two really should be kref_init because the kref is being
initialised.

This suggests that making kref_set available encourages bad code.
So fix the three uses and remove kref_set completely.

Signed-off-by: NeilBrown <[email protected]>
Acked-by: Mimi Zohar <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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