Messages in this thread | | | Date | Wed, 14 May 2014 12:07:05 +0200 | From | Peter Zijlstra <> | Subject | Re: [patch 0/3] futex/rtmutex: Fix issues exposed by trinity |
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On Wed, May 14, 2014 at 11:53:44AM +0200, Thomas Gleixner wrote: > > What error would we return? > > > > This particular case is a serious error for which we have no good error code > > to return to userspace. It's an implementation defect, a bug, we should probably > > assert instead of pausing. > > Errm. > > http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_mutex_lock.html > > The pthread_mutex_lock() function may fail if: > > [EDEADLK] > The current thread already owns the mutex. > > That's a exactly the error code, which the kernel returns when it > detects a deadlock. > > And glibc returns EDEADLK at a lot of places already. So in that case > it's not a serious error? Because it's detected by glibc. You can't be > serious about that. > > So why is a kernel detected deadlock different? Because it detects not > only AA, it detects ABBA and more. But it's still a dead lock. And > while posix spec only talks about AA, it's the very same issue. > > So why not propagate this to the caller so he gets an alert right away > instead of letting him attach a debugger, and scratch his head and > lookup glibc source to find out why the hell glibc called pause.
http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_mutex_lock.html
The pthread_mutex_lock() function may fail if:
[EDEADLK] A deadlock condition was detected or the current thread already owns the mutex.
Which is explicitly wider than the AA recursion and fully supports the full lock graph traversal we do. [unhandled content-type:application/pgp-signature] | |