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SubjectRe: Multi-thread corefiles broken since April
Hi Steve,

please open a bug at http://bugzilla.kernel.org/ for this issue so that
it doesn't get lost.

@Stas:
It was your patch that broke it, can you look into it?

TIA
Adrian


On Wed, Dec 07, 2005 at 10:52:52PM -0800, Steve Work wrote:
> Coredumps from programs with more than one thread show garbage
> information for all threads except the primary. The problem was
> introduced with:
>
> http://kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=5df240826c90afdc7956f55a004ea6b702df9203
>
> on Apr 16 ("fix crash in entry.S restore_all") and is still present in
> current builds.
>
> "kill -SEGV" this program and "info threads" the resulting corefile to
> see the problem:
>
> #include <pthread.h>
> static void* thread_sleep(void* x) { while (1) sleep(30); }
> int main(int c, char** v) {
> const static int tcount = 5;
> pthread_t thr[tcount];
> int i;
> for (i=0; i<tcount; ++i)
> pthread_create(&thr[i], NULL, thread_sleep, NULL);
> while (1)
> sleep(30);
> return 0;
> }
>
> (gdb) info threads
> 7 process 18138 0x00000246 in ?? ()
> 6 process 18139 0x00000246 in ?? ()
> 5 process 18140 0x00000246 in ?? ()
> 4 process 18141 0x00000246 in ?? ()
> 3 process 18142 0x00000246 in ?? ()
> 2 process 18143 0x00000246 in ?? ()
> * 1 process 18137 0xb7e69db6 in nanosleep () from /lib/tls/libc.so.6
> (gdb)
>
> All these threads should show a legitimate location (the same spot in
> nanosleep) and do on kernels prior to the commit named above. (Notice
> one too many threads listed here also -- is this a related problem?)
>
> Commenting out this line (in asm/i386/kernel/process.c:copy_thread)
> fixes the corefiles:
>
> childregs = (struct pt_regs *) ((unsigned long) childregs - 8);
>
> but presumably re-introduces the crash the original patch was intended
> to fix. Should this line be conditioned somehow? Or do the corefile
> write routines need to know about this adjusted offset?
>
> Steve Work
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