devres: Fix page faults when tracing devres from unloaded modules

The devres ftrace event logs the name of the devres node, which is often a
function name (e.g., "devm_work_drop") stringified by mac

devres: Fix page faults when tracing devres from unloaded modules

The devres ftrace event logs the name of the devres node, which is often a
function name (e.g., "devm_work_drop") stringified by macros like
devm_add_action. Currently, ftrace stores this name as a string literal
address, which can become invalid when the module containing the string is
unloaded. This results in page faults when ftrace tries to access the name.

This behavior is problematic because the devres ftrace event is designed to
trace resource management throughout a device driver's lifecycle, including
during module unload. The event should be available even after the module
is unloaded to properly diagnose resource issues.

Fix the issue by copying the devres node name into the ftrace ring buffer
using __assign_str(), instead of storing just the address. This ensures
that ftrace can always access the name, even if the module is unloaded.

This change increases the memory usage for each of the ftrace entry by
12-16 bytes assuming the average devres node name is 20 bytes long,
depending on the size of const char *.

Note that this change does not affect anything unless all of following
conditions are met.
- CONFIG_DEBUG_DEVRES is enabled
- ftrace tracing is enabled
- The devres event is enabled in ftrace tracing

Fixes: 09705dcb63d2 ("devres: Enable trace events")
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Keita Morisaki <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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tracing/treewide: Remove second parameter of __assign_str()

With the rework of how the __string() handles dynamic strings where it
saves off the source string in field in the helper structure[1], th

tracing/treewide: Remove second parameter of __assign_str()

With the rework of how the __string() handles dynamic strings where it
saves off the source string in field in the helper structure[1], the
assignment of that value to the trace event field is stored in the helper
value and does not need to be passed in again.

This means that with:

__string(field, mystring)

Which use to be assigned with __assign_str(field, mystring), no longer
needs the second parameter and it is unused. With this, __assign_str()
will now only get a single parameter.

There's over 700 users of __assign_str() and because coccinelle does not
handle the TRACE_EVENT() macro I ended up using the following sed script:

git grep -l __assign_str | while read a ; do
sed -e 's/\(__assign_str([^,]*[^ ,]\) *,[^;]*/\1)/' $a > /tmp/test-file;
mv /tmp/test-file $a;
done

I then searched for __assign_str() that did not end with ';' as those
were multi line assignments that the sed script above would fail to catch.

Note, the same updates will need to be done for:

__assign_str_len()
__assign_rel_str()
__assign_rel_str_len()

I tested this with both an allmodconfig and an allyesconfig (build only for both).

[1] https://lore.kernel.org/linux-trace-kernel/[email protected]/

Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Julia Lawall <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
Acked-by: Jani Nikula <[email protected]>
Acked-by: Christian König <[email protected]> for the amdgpu parts.
Acked-by: Thomas Hellström <[email protected]> #for
Acked-by: Rafael J. Wysocki <[email protected]> # for thermal
Acked-by: Takashi Iwai <[email protected]>
Acked-by: Darrick J. Wong <[email protected]> # xfs
Tested-by: Guenter Roeck <[email protected]>

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devres: Enable trace events

In some cases the printf() mechanism is too heavy and can't be used.
For example, when debugging a race condition involving devres API.
When CONFIG_DEBUG_DEVRES is enable

devres: Enable trace events

In some cases the printf() mechanism is too heavy and can't be used.
For example, when debugging a race condition involving devres API.
When CONFIG_DEBUG_DEVRES is enabled I can't reproduce an issue, and
otherwise it's quite visible with a useful information being collected.

Enable trace events for devres part of the driver core.

Signed-off-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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