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signal: sigprocmask() should do retarget_shared_pending()
In short, almost every changing of current->blocked is wrong, or at least can lead to the unexpected results. For example. Two threads T1 and T2, T1 sleeps in sigtimedwait/pause/etc. kill(tgid, SIG) can pick T2 for TIF_SIGPENDING. If T2 calls sigprocmask() and blocks SIG before it notices the pending signal, nobody else can handle this pending shared signal. I am not sure this is bug, but at least this looks strange imho. T1 should not sleep forever, there is a signal which should wake it up. This patch moves the code which actually changes ->blocked into the new helper, set_current_blocked() and changes this code to call retarget_shared_pending() as exit_signals() does. We should only care about the signals we just blocked, we use "newset & ~current->blocked" as a mask. We do not check !sigisemptyset(newblocked), retarget_shared_pending() is cheap unless mask & shared_pending. Note: for this particular case we could simply change sigprocmask() to return -EINTR if signal_pending(), but then we should change other callers and, more importantly, if we need this fix then set_current_blocked() will have more callers and some of them can't restart. See the next patch as a random example. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com> Acked-by: Tejun Heo <tj@kernel.org>
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2 changed files with 25 additions and 5 deletions
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@ -243,6 +243,7 @@ extern long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig,
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siginfo_t *info);
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extern long do_sigpending(void __user *, unsigned long);
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extern int sigprocmask(int, sigset_t *, sigset_t *);
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extern void set_current_blocked(const sigset_t *);
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extern int show_unhandled_signals;
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struct pt_regs;
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@ -2299,6 +2299,29 @@ long do_no_restart_syscall(struct restart_block *param)
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return -EINTR;
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}
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/**
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* set_current_blocked - change current->blocked mask
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* @newset: new mask
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*
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* It is wrong to change ->blocked directly, this helper should be used
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* to ensure the process can't miss a shared signal we are going to block.
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*/
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void set_current_blocked(const sigset_t *newset)
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{
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struct task_struct *tsk = current;
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spin_lock_irq(&tsk->sighand->siglock);
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if (signal_pending(tsk) && !thread_group_empty(tsk)) {
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sigset_t newblocked;
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/* A set of now blocked but previously unblocked signals. */
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signandsets(&newblocked, newset, ¤t->blocked);
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retarget_shared_pending(tsk, &newblocked);
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}
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tsk->blocked = *newset;
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recalc_sigpending();
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spin_unlock_irq(&tsk->sighand->siglock);
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}
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/*
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* This is also useful for kernel threads that want to temporarily
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* (or permanently) block certain signals.
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@ -2330,11 +2353,7 @@ int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
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return -EINVAL;
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}
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spin_lock_irq(&tsk->sighand->siglock);
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tsk->blocked = newset;
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recalc_sigpending();
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spin_unlock_irq(&tsk->sighand->siglock);
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set_current_blocked(&newset);
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return 0;
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}
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