Messages in this thread Patch in this message | | | Subject | [PATCH] fix for zeroed user-space tids in multi-threaded core dumps | Date | Wed, 25 Oct 2006 21:41:42 -0400 | From | Ernie Petrides <> |
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Hi, Andrew. Please consider the patch below for the next open 2.6 release.
The NPTL library uses the CLONE_CHILD_CLEARTID flag on clone() syscalls on behalf of pthread_create() library calls. This feature is used to request that the kernel clear the thread-id in user space (at an address provided in the syscall) when the thread disassociates itself from the address space, which is done in mm_release().
Unfortunately, when a multi-threaded process incurs a core dump (such as from a SIGSEGV), the core-dumping thread sends SIGKILL signals to all of the other threads, which then proceed to clear their user-space tids before synchronizing in exit_mm() with the start of core dumping. This misrepresents the state of process's address space at the time of the SIGSEGV and makes it more difficult for someone to debug NPTL and glibc problems (misleading him/her to conclude that the threads had gone away before the fault).
The fix below is to simply avoid the CLONE_CHILD_CLEARTID action if a core dump has been initiated.
Cheers. -ernie
--- linux-2.6.18/kernel/fork.c.orig +++ linux-2.6.18/kernel/fork.c @@ -439,7 +439,9 @@ void mm_release(struct task_struct *tsk, tsk->vfork_done = NULL; complete(vfork_done); } - if (tsk->clear_child_tid && atomic_read(&mm->mm_users) > 1) { + if (tsk->clear_child_tid && + mm->core_waiters == 0 && + atomic_read(&mm->mm_users) > 1) { u32 __user * tidptr = tsk->clear_child_tid; tsk->clear_child_tid = NULL; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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