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| author | Oleg Nesterov <oleg@redhat.com> | 2011-04-27 20:59:41 +0200 |
|---|---|---|
| committer | Oleg Nesterov <oleg@redhat.com> | 2011-04-28 13:01:37 +0200 |
| commit | e6fa16ab9c1e9b344428e6fea4d29e3cc4b28fb0 (patch) | |
| tree | c1bdacc0537213cba8ba75a63ac286e21c0a7250 | |
| parent | 73ef4aeb61b53fce464a7e24ef03a26f98b2f617 (diff) | |
| download | linux-3.10-e6fa16ab9c1e9b344428e6fea4d29e3cc4b28fb0.tar.gz linux-3.10-e6fa16ab9c1e9b344428e6fea4d29e3cc4b28fb0.tar.bz2 linux-3.10-e6fa16ab9c1e9b344428e6fea4d29e3cc4b28fb0.zip | |
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>
| -rw-r--r-- | include/linux/signal.h | 1 | ||||
| -rw-r--r-- | kernel/signal.c | 29 |
2 files changed, 25 insertions, 5 deletions
diff --git a/include/linux/signal.h b/include/linux/signal.h index fcd2b14b193..ba009c16727 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -243,6 +243,7 @@ extern long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info); extern long do_sigpending(void __user *, unsigned long); extern int sigprocmask(int, sigset_t *, sigset_t *); +extern void set_current_blocked(const sigset_t *); extern int show_unhandled_signals; struct pt_regs; diff --git a/kernel/signal.c b/kernel/signal.c index e8308e3238c..8aa3a2e226a 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2299,6 +2299,29 @@ long do_no_restart_syscall(struct restart_block *param) return -EINTR; } +/** + * set_current_blocked - change current->blocked mask + * @newset: new mask + * + * It is wrong to change ->blocked directly, this helper should be used + * to ensure the process can't miss a shared signal we are going to block. + */ +void set_current_blocked(const sigset_t *newset) +{ + struct task_struct *tsk = current; + + spin_lock_irq(&tsk->sighand->siglock); + if (signal_pending(tsk) && !thread_group_empty(tsk)) { + sigset_t newblocked; + /* A set of now blocked but previously unblocked signals. */ + signandsets(&newblocked, newset, ¤t->blocked); + retarget_shared_pending(tsk, &newblocked); + } + tsk->blocked = *newset; + recalc_sigpending(); + spin_unlock_irq(&tsk->sighand->siglock); +} + /* * This is also useful for kernel threads that want to temporarily * (or permanently) block certain signals. @@ -2330,11 +2353,7 @@ int sigprocmask(int how, sigset_t *set, sigset_t *oldset) return -EINVAL; } - spin_lock_irq(&tsk->sighand->siglock); - tsk->blocked = newset; - recalc_sigpending(); - spin_unlock_irq(&tsk->sighand->siglock); - + set_current_blocked(&newset); return 0; } |