[Linux-ia64] Re: pthread_mutex_lock sometimes fails on Linux 2.4.5

[Linux-ia64] Re: pthread_mutex_lock sometimes fails on Linux 2.4.5

[Bill Nottingham]

Robboy, David G (david.g.robboy@intel.com) said: 
> On a 4P Lion with Red Hat 7.0.98 installed and a 2.4.5 kernel, a 4P fft
> application sometimes hangs in a barrier.  All 4 threads get into the
> barrier and none get out because a count gets up to 3 and they are waiting
> for it to get to 4.

Stock 2.4.5 or something else?

Bill

RE: [Linux-ia64] Re: pthread_mutex_lock sometimes fails on Linux

[Robboy, David G]

> Stock 2.4.5 or something else?

Something else.  We have features of our own in the kernel for system
validation.  I guess I should try it on a stock kernel.

David

RE: [Linux-ia64] Re: pthread_mutex_lock sometimes fails on Linux

[Robboy, David G]

The problem I previously reported occurs on a 2.4.5 kernel built from stock
source code (No Alan Cox patches, only the ia64 patch).

I slightly misstated the problem.  Here is what actually happens:
Four threads have entered a barrier (my own C code).  Within the barrier,
they call pthread_mutex_lock and increment a counter while holding the lock.
Three threads are waiting on the counter, whose value is three, to go to
four.  The fourth CPU is looping in the kernel in cpu_idle.  I don't know
how it got there, but probably it has something to do with calling
pthread_mutex_lock.

As I said, if anyone wants to investigate this I will provide a test case.

David

> -----Original Message-----
> From: Robboy, David G [mailto:david.g.robboy@intel.com]
> Sent: Wednesday, June 27, 2001 11:30 AM
> To: 'Bill Nottingham'; 'linux-ia64@linuxia64.org'
> Subject: RE: [Linux-ia64] Re: pthread_mutex_lock sometimes fails on
> Linux 2.4.5
> 
> 
> > Stock 2.4.5 or something else?
> 
> Something else.  We have features of our own in the kernel for system
> validation.  I guess I should try it on a stock kernel.
> 
> David
> 
> 
> _______________________________________________
> Linux-IA64 mailing list
> Linux-IA64@linuxia64.org
> http://lists.linuxia64.org/lists/listinfo/linux-ia64
> 

RE: [Linux-ia64] Re: pthread_mutex_lock sometimes fails on Linux

[Luck, Tony]

This sounds similar to a problem that I saw a few weeks
ago.  In my case threads would spin for an inordinate
amount of time in __pthread_lock() because re-reading of
the __status field was optimised out of the loop (it isn't
declared as volatile).  Newer versions of glibc (2.2.2 IIRC)
have some __asm() magic in the loop to force the re-read (the
glibc folks didn't want to make the __status field volatile
because of lots of other pointer casting changes that would
have been needed).

See if a newer glibc helps with your problem too.

-Tony Luck

-----Original Message-----
I slightly misstated the problem.  Here is what actually happens:
Four threads have entered a barrier (my own C code).  Within the barrier,
they call pthread_mutex_lock and increment a counter while holding the lock.
Three threads are waiting on the counter, whose value is three, to go to
four.  The fourth CPU is looping in the kernel in cpu_idle.  I don't know
how it got there, but probably it has something to do with calling
pthread_mutex_lock.

[Linux-ia64] Re: pthread_mutex_lock sometimes fails on Linux 2.4.5

[Jose Luu]

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> As I said, if anyone wants to investigate this I will provide a test case.
>
> David

I am seeing something similar in ia32 mode, in my case, this is not new (saw it since 2.4.1).

Could you send me your test case ? As it may help me to investigate.

Thanks
Jose


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