[lkml]   [2010]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRE: Serious problem with ticket spinlocks on ia64
> Hedi Berriche sent me a simple test case that can
> trigger the failure on the siglock.

Can you post the test case please. How long does it typically take
to reproduce the problem?

> Next, CPU 5 releases the spinlock with st2.rel, changing the lock
> value to 0x0 (correct).
> Now, CPU 4, CPU 5 and CPU 7 all want to acquire the lock again.
> Interestingly, CPU 5 and CPU 7 are both granted the same ticket,

What is the duplicate ticket number that CPUs 5 & 7 get at this point?
Presumably 0x0, yes? Or do they see a stale 0x7fff?

> and the spinlock value (as seen from the debug fault handler) is
> 0x0 after single-stepping over the fetchadd4.acq, in both cases.
> CPU 4 correctly sets the spinlock value to 0x1.

Is the fault handler using "ld.acq" to look at the spinlock value?
If not, then this might be a red herring. [Though clearly something
bad is going on here].

> Any ideas?

What cpu model are you running on?
What is the topological connection between CPU 4, 5 and 7 - are any of
them hyper-threaded siblings? Cores on same socket? N.B. topology may
change from boot to boot, so you may need to capture /proc/cpuinfo from
the same boot where this problem is detected. But the variation is
usually limited to which socket gets to own logical cpu 0.

If this is a memory ordering problem (and that seems quite plausible)
then a liberal sprinkling of "ia64_mf()" calls throughout the spinlock
routines would probably make it go away.


 \ /
  Last update: 2010-08-27 18:11    [W:0.080 / U:1.844 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site