linux-kernel - Re: [PATCH] kselftest: Mark functions that unconditionally call exit() as _

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Date: Thu, 11 Apr 2024 15:11:07 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Nathan Chancellor <nathan@...nel.org>, tglx@...utronix.de,
 shuah@...nel.org, Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: oleg@...hat.com, anna-maria@...utronix.de, frederic@...nel.org,
 ndesaulniers@...gle.com, morbo@...gle.com, justinstitt@...gle.com,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 llvm@...ts.linux.dev, patches@...ts.linux.dev,
 John Stultz <jstultz@...gle.com>, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] kselftest: Mark functions that unconditionally call
 exit() as __noreturn

On 4/11/24 12:45, Nathan Chancellor wrote:
> After commit 6d029c25b71f ("selftests/timers/posix_timers: Reimplement
> check_timer_distribution()"), clang warns:
> 
>    tools/testing/selftests/timers/../kselftest.h:398:6: warning: variable 'major' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
>      398 |         if (uname(&info) || sscanf(info.release, "%u.%u.", &major, &minor) != 2)
>          |             ^~~~~~~~~~~~
>    tools/testing/selftests/timers/../kselftest.h:401:9: note: uninitialized use occurs here
>      401 |         return major > min_major || (major == min_major && minor >= min_minor);
>          |                ^~~~~
>    tools/testing/selftests/timers/../kselftest.h:398:6: note: remove the '||' if its condition is always false
>      398 |         if (uname(&info) || sscanf(info.release, "%u.%u.", &major, &minor) != 2)
>          |             ^~~~~~~~~~~~~~~
>    tools/testing/selftests/timers/../kselftest.h:395:20: note: initialize the variable 'major' to silence this warning
>      395 |         unsigned int major, minor;
>          |                           ^
>          |                            = 0
> 
> This is a false positive because if uname() fails, ksft_exit_fail_msg()
> will be called, which unconditionally calls exit(), a noreturn function.
> However, clang does not know that ksft_exit_fail_msg() will call exit()
> at the point in the pipeline that the warning is emitted because
> inlining has not occurred, so it assumes control flow will resume
> normally after ksft_exit_fail_msg() is called.
> 
> Make it clear to clang that all of the functions that call exit()
> unconditionally in kselftest.h are noreturn transitively by marking them
> explicitly with '__attribute__((__noreturn__))', which clears up the
> warning above and any future warnings that may appear for the same
> reason.
> 
> Fixes: 6d029c25b71f ("selftests/timers/posix_timers: Reimplement check_timer_distribution()")
> Reported-by: John Stultz <jstultz@...gle.com>
> Closes: https://lore.kernel.org/all/20240410232637.4135564-2-jstultz@google.com/
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> I have based this change on timers/urgent, as the commit that introduces
> this particular warning is there and it is marked for stable, even
> though this appears to be a generic kselftest issue. I think it makes
> the most sense for this change to go via timers/urgent with Shuah's ack.
> While __noreturn with a return type other than 'void' does not make much
> sense semantically, there are many places that these functions are used
> as the return value for other functions such as main(), so I did not
> change the return type of these functions from 'int' to 'void' to
> minimize the necessary changes for a backport (it is an existing issue
> anyways).
> 
> I see there is another instance of this problem that will need to be
> addressed in -next, introduced by commit f07041728422 ("selftests: add
> ksft_exit_fail_perror()").

Thank you. Assuming this is going through tip/timers/urgent

Acked-by: Shuah Khan <skhan@...uxfoundation.org>

Usama, please send patch fixing this problem in next on top of

commit f07041728422 ("selftests: add
> ksft_exit_fail_perror()").

thanks,
-- Shuah