[PATCH] Add compiler barriers around modifications of the robust mutex list for pthread_mutex_trylock.

[Stefan Liebler]

Hi,

while debugging a kernel warning, Thomas Gleixner, Sebastian Sewior and
Heiko Carstens found a bug in pthread_mutex_trylock due to misordered
instructions:
140:   a5 1b 00 01             oill    %r1,1
144:   e5 48 a0 f0 00 00       mvghi   240(%r10),0   <--- THREAD_SETMEM 
(THREAD_SELF, robust_head.list_op_pending, NULL);
14a:   e3 10 a0 e0 00 24       stg     %r1,224(%r10) <--- last 
THREAD_SETMEM of ENQUEUE_MUTEX_PI

vs (with compiler barriers):
140:   a5 1b 00 01             oill    %r1,1
144:   e3 10 a0 e0 00 24       stg     %r1,224(%r10)
14a:   e5 48 a0 f0 00 00       mvghi   240(%r10),0

Please have a look at the discussion:
"Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggerede"
(https://lore.kernel.org/lkml/20190202112006.GB3381@osiris/)

This patch is introducing the same compiler barriers and comments
for pthread_mutex_trylock as introduced for pthread_mutex_lock and
pthread_mutex_timedlock by commit 8f9450a0b7a9e78267e8ae1ab1000ebca08e473e
"Add compiler barriers around modifications of the robust mutex list."

Okay to commit?

The original commit was first available with glibc release 2.25.
Once this patch is committed, we should at least backport it to
glibc release branches 2.25 - 2.28?

Does anybody know if and where the original commit was backported to?
I've found at least "Bug 1401665 - Fix process shared robust mutex 
defects." (https://bugzilla.redhat.com/show_bug.cgi?id=1401665#c34)

Bye
Stefan

ChangeLog:

	* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
	Add compiler barriers and comments.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20190205_pthread_mutex_trylock_barriers.patch
Type: text/x-patch
Size: 6792 bytes
Desc: not available
URL: <http://sourceware.org/pipermail/libc-alpha/attachments/20190205/ced41bd5/attachment.bin>