pthread_mutex_lock sometimes fails on Linux 2.4.5

Stock 2.4.5 or something else?

Bill

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

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

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.

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