Messages in this thread | | | Date | Thu, 21 Jun 2007 12:25:09 +0400 | From | Oleg Nesterov <> | Subject | Re: Fix signalfd interaction with thread-private signals |
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On 06/20, Linus Torvalds wrote: > > On Wed, 20 Jun 2007, Oleg Nesterov wrote: > > > > Also, suppose that some thread does > > > > for (;;) > > signal(SIGSEGV, SIG_IGN); > > > > Now we have the same situation. do_sigaction() can steal SIGSEGV from > > another thread. > > Actually, that shouldn't be possible. > > See "force_sig_info()". It does not allow blocking or ignoring forced > signals. We will reset such a signal handler to SIG_DFL, and unlock it. > > So if you get a SIGSEGV while SIGSEGV's are blocked or ignored, the kernel > *will* kill you. No questions asked.
Yes, and no.
Yes, force_sig() unblocks and un-ignores the signal. However, unlike group-wide signals, thread-specific signals do not convert themselves to SIGKILL on delivery. The target thread should dequeue SIGSEGV and then it calls do_group_exit(). Before it does so, another thread doing signal(SIGSEGV, SIG_IGN) can steal the signal.
Of course, this is unlikely, and the target thread will take page fault again. The same for signalfd.
Oleg.
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