Messages in this thread | | | Date | Wed, 14 May 2014 12:28:09 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch 0/3] futex/rtmutex: Fix issues exposed by trinity |
| |
On Wed, 14 May 2014, Peter Zijlstra wrote: > 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
Yuck. I should not have used the first link Gurgle brought up.
> 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.
Definitely. It's what the kernel does :)
Thanks,
tglx
| |