[REPOST] Multi-thread corefiles broken since April
- From: Steve Work <swork@xxxxxxxxxxxx>
- Date: Fri, 09 Dec 2005 10:49:20 -0800
Q: When did *all* multi-thread userspace coredumps break?
A: 2.6.12-rc3, specifically April 16; and they're still broken (really!) Config does not appear to matter. Not a race: highly reproduceable, see below.
-------- Original Message -------- Subject: Multi-thread corefiles broken since April Date: Wed, 07 Dec 2005 22:52:52 -0800 From: Steve Work <swork@xxxxxxxxxxxx> To: linux-kernel@xxxxxxxxxxxxxxx
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?
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