Commit e6fa16ab authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

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: default avatarOleg Nesterov <>
Reviewed-by: default avatarMatt Fleming <>
Acked-by: default avatarTejun Heo <>
parent 73ef4aeb
......@@ -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;
......@@ -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;
if (signal_pending(tsk) && !thread_group_empty(tsk)) {
sigset_t newblocked;
/* A set of now blocked but previously unblocked signals. */
signandsets(&newblocked, newset, &current->blocked);
retarget_shared_pending(tsk, &newblocked);
tsk->blocked = *newset;
* 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;
tsk->blocked = newset;
return 0;
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment