Messages in this thread Patch in this message | | | Date | Wed, 23 Nov 2005 17:24:08 +0300 | From | Oleg Nesterov <> | Subject | [PATCH] do_coredump() should reset group_stop_count earlier |
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__group_complete_signal() sets ->group_stop_count in sig_kernel_coredump() path and marks the target thread as ->group_exit_task. So any thread except group_exit_task will go to handle_group_stop()->finish_stop().
However, when group_exit_task actually starts do_coredump(), it sets SIGNAL_GROUP_EXIT, but does not reset ->group_stop_count while killing other threads. If we have not yet stopped threads in the same thread group, they all will spin in kernel mode until group_exit_task sends them SIGKILL, because ->group_stop_count > 0 means:
recalc_sigpending_tsk() never clears TIF_SIGPENDING
get_signal_to_deliver() goes to handle_group_stop()
handle_group_stop() returns when SIGNAL_GROUP_EXIT set
syscall_exit/resume_userspace notice TIF_SIGPENDING, call get_signal_to_deliver() again.
So we are wasting cpu cycles, and if one of these threads is rt_task() this may be a serious problem.
NOTE: do_coredump() holds ->mmap_sem, so not stopped threads can't escape coredumping after clearing ->group_stop_count.
See also this thread: http://marc.theaimsgroup.com/?t=112739139900002
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 2.6.15-rc2/fs/exec.c~ 2005-11-23 19:23:15.000000000 +0300 +++ 2.6.15-rc2/fs/exec.c 2005-11-23 19:56:07.000000000 +0300 @@ -1472,6 +1472,7 @@ int do_coredump(long signr, int exit_cod if (!(current->signal->flags & SIGNAL_GROUP_EXIT)) { current->signal->flags = SIGNAL_GROUP_EXIT; current->signal->group_exit_code = exit_code; + current->signal->group_stop_count = 0; retval = 0; } spin_unlock_irq(¤t->sighand->siglock); @@ -1487,7 +1488,6 @@ int do_coredump(long signr, int exit_cod * Clear any false indication of pending signals that might * be seen by the filesystem code called to write the core file. */ - current->signal->group_stop_count = 0; clear_thread_flag(TIF_SIGPENDING); if (current->signal->rlim[RLIMIT_CORE].rlim_cur < binfmt->min_coredump) - 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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