[PATCH] do_coredump() should reset group_stop_count earlier
__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>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 file changed