[asterisk-dev] [Code Review] 4247: DEBUG_THREADS: Fix regression and lock tracking initialization problems.

[rmudgett]

> On Dec. 8, 2014, 7:53 p.m., Matt Jordan wrote:
> > /branches/1.8/main/lock.c, lines 135-141
> > <https://reviewboard.asterisk.org/r/4247/diff/2/?file=69604#file69604line135>
> >
> >     Given the code in __ast_rwlock_init, I'm not sure this code should still be commented out. Going _way_ back in time, we have the following when this was committed:
> >     
> >     ------------------------------------------------------------------------
> >     r87740 | tilghman | 2007-10-30 18:08:59 -0500 (Tue, 30 Oct 2007) | 13 lines
> >     
> >     Merged revisions 87739 via svnmerge from 
> >     https://origsvn.digium.com/svn/asterisk/branches/1.4
> >     
> >     ........
> >     r87739 | tilghman | 2007-10-30 18:02:22 -0500 (Tue, 30 Oct 2007) | 5 lines
> >     
> >     Fix for uninitialized mutexes on *BSD
> >     Reported by: ys
> >     Fixed by: ys
> >     Closes issue #11116
> >     
> >     ........
> >     
> >     ------------------------------------------------------------------------
> >     
> >     
> >     I think we should either remove the commented out code, or uncomment it. Since this exists in similar mutex initialization, I'd say uncomment it.

Considering that I removed the DEBUG_THREADS "helper" indirect mutex initialization code, you are right that it probably should be uncommented now.


- rmudgett


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On Dec. 8, 2014, 6:17 p.m., rmudgett wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/4247/
> -----------------------------------------------------------
> 
> (Updated Dec. 8, 2014, 6:17 p.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Bugs: ASTERISK-19463 and ASTERISK-22455
>     https://issues.asterisk.org/jira/browse/ASTERISK-19463
>     https://issues.asterisk.org/jira/browse/ASTERISK-22455
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> This patch started with David Lee's patch at
> https://reviewboard.asterisk.org/r/2826/ and includes a regression fix
> introduced by the ASTERISK-22455 patch.
> 
> The initialization of a mutex's lock tracking structure was not protected
> in a critical section.  This is fine for any mutex that is explicitly
> initialized, but a static mutex may have its lock tracking double
> initialized if multiple threads attempt the first lock simultaneously.
> 
> * Added a global mutex to properly serialize initialization of the lock
> tracking structure.  The painful global lock can be mitigated by adding a
> double checked lock flag as discussed on the original review request.
> 
> * Defer lock tracking initialization until first use.
> 
> * Don't be "helpful" and initialize an uninitialized lock when
> DEBUG_THREADS is enabled.  Debug code is not supposed to fix or change
> normal code behavior.  We don't need a lock initialization race that would
> force a re-setup of lock tracking.  Lock tracking already handles
> initialization on first use.
> 
> * Properly handle allocation failures of the lock tracking structure.
> 
> * No need to initialize tracking data in __ast_pthread_mutex_destroy()
> just to turn around and destroy it.
> 
> 
> The regression introduced by ASTERISK-22455 is the result of manipulating
> a pthread_mutex_t struct outside of the pthread library code.  The
> pthread_mutex_t struct seems to have a global linked list pointer member
> that can get changed by other threads.  Therefore, saving and restoring
> the contents of a pthread_mutex_t struct is a bad thing.
> 
> Thanks to Thomas Airmont for finding this obscure regression.
> 
> * Don't overwrite the struct ast_lock_track.reentr_mutex member to restore
> tracking data in __ast_cond_wait() and __ast_cond_timedwait().  The
> pthread_mutex_t struct must be treated as a read-only opaque variable.
> 
> 
> Miscellaneous other items fixed by this patch:
> 
> * Match ast_suspend_lock_info() with ast_restore_lock_info() in
> __ast_cond_timedwait().
> 
> * Made some uninitialized lock sanity checks return EINVAL and try a
> DO_THREAD_CRASH.
> 
> * Fix bad canlog initialization expressions.
> 
> 
> NOTE: The first diff on this review is the unmodified
> https://reviewboard.asterisk.org/r/2826/ patch for comparison with the
> updated patch.
> 
> 
> Diffs
> -----
> 
>   /branches/1.8/main/lock.c 429126 
>   /branches/1.8/include/asterisk/lock.h 429126 
> 
> Diff: https://reviewboard.asterisk.org/r/4247/diff/
> 
> 
> Testing
> -------
> 
> Without the patch on v1.8, I repeatedly ran the testsuite masquerade
> supertest and it died an hour or two later.  With the patch, it ran over
> the weekend without a problem.
> 
> Since the DEBUG_THREADS locking issues on Asterisk startup
> (ASTERISK-19463) have been a hard problem to reproduce, I propose we setup
> Bamboo to run the TestSuite with DEBUG_THREADS enabled on the
> http://svn.asterisk.org/svn/asterisk/team/rmudgett/debug_threads branch
> nightly for a few weeks.
> 
> 
> Thanks,
> 
> rmudgett
> 
>

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