Subject: Re: race condition in pthread write()?
To: Karl Janmar <email@example.com>
From: Nathan J. Williams <firstname.lastname@example.org>
Date: 02/11/2003 13:28:53
Karl Janmar <email@example.com> writes:
> Here is some more data:
> (gdb) info thread
> 5 Thread 0 0x485700f7 in poll () from /usr/lib/libc.so.12
> 4 Thread 21 0x4857008b in select () from /usr/lib/libc.so.12
> 3 Thread 22 0x4857013f in nanosleep () from /usr/lib/libc.so.12
> 2 Thread 69 0x4857013f in nanosleep () from /usr/lib/libc.so.12
> * 1 Thread 70 0x482e5f65 in write () from /usr/lib/libpthread.so.0
> (gdb) thread ex all
> 0x48fc0000: thread 70 in kernel
> 0x48f80000: thread 69 in kernel
> 0x48f40000: thread 22 in kernel
> 0x48b40000: thread 21 in kernel
> 0xbfbc0000: thread 0 in kernel
OK. All the userland threads are sleeping in the kernel (actually,
they probably woke up from their original system call, tried to
deliver a UNBLOCKED upcall, and are sleeping waiting for a stack to
become avaliable). The fact that there's still a thread consuming CPU
probably means another bug in libpthread.. possibly in the
resolve_locks dance in pthread_sa.c; more likely a spinlock count is
going negative somewhere, which will confuse the resolve_locks algorithm.
This is i386, right (guessing from the address of thread 0)? I'll send
you some additional debugging tools in a little bit.
> If I get the point the sa_nstacks is running out because the stacks aren't
> recycle properly, so someware in kern_sa.c it "leaks stacks"?
That's one possibility... more likely, though, is that the userland
code is wedged in a state where it doesn't get around to recycling the
used stacks back to the kernel.