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Oleg Nesterov authored
commit 3245d6ac upstream. wait_consider_task() checks EXIT_ZOMBIE after EXIT_DEAD/EXIT_TRACE and both checks can fail if we race with EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE change in between, gcc needs to reload p->exit_state after security_task_wait(). In this case ->notask_error will be wrongly cleared and do_wait() can hang forever if it was the last eligible child. Many thanks to Arne who carefully investigated the problem. Note: this bug is very old but it was pure theoretical until commit b3ab0316 ("wait: completely ignore the EXIT_DEAD tasks"). Before this commit "-O2" was probably enough to guarantee that compiler won't read ->exit_state twice. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reported-by: Arne Goedeke <el@laramies.com> Tested-by: Arne Goedeke <el@laramies.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
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