From 7bb44adef39ad3bda2be40bb34686bc56bd563a5 Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Wed, 23 May 2007 13:57:44 -0700 Subject: [PATCH] recalc_sigpending_tsk fixes Steve Hawkes discovered a problem where recalc_sigpending_tsk was called in do_sigaction but no signal_wake_up call was made, preventing later signals from waking up blocked threads with TIF_SIGPENDING already set. In fact, the few other calls to recalc_sigpending_tsk outside the signals code are also subject to this problem in other race conditions. This change makes recalc_sigpending_tsk private to the signals code. It changes the outside calls, as well as do_sigaction, to use the new recalc_sigpending_and_wake instead. Signed-off-by: Roland McGrath Cc: Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/sched.h | 12 +++++++----- kernel/exit.c | 7 ++----- kernel/power/process.c | 2 +- kernel/signal.c | 24 ++++++++++++++++++------ 4 files changed, 28 insertions(+), 17 deletions(-) Index: b/include/linux/sched.h =================================================================== --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1591,11 +1591,13 @@ static inline int lock_need_resched(spin return 0; } -/* Reevaluate whether the task has signals pending delivery. - This is required every time the blocked sigset_t changes. - callers must hold sighand->siglock. */ - -extern FASTCALL(void recalc_sigpending_tsk(struct task_struct *t)); +/* + * Reevaluate whether the task has signals pending delivery. + * Wake the task if so. + * This is required every time the blocked sigset_t changes. + * callers must hold sighand->siglock. + */ +extern void recalc_sigpending_and_wake(struct task_struct *t); extern void recalc_sigpending(void); extern void signal_wake_up(struct task_struct *t, int resume_stopped); Index: b/kernel/exit.c =================================================================== --- a/kernel/exit.c +++ b/kernel/exit.c @@ -751,11 +751,8 @@ static void exit_notify(struct task_stru read_lock(&tasklist_lock); spin_lock_irq(&tsk->sighand->siglock); for (t = next_thread(tsk); t != tsk; t = next_thread(t)) - if (!signal_pending(t) && !(t->flags & PF_EXITING)) { - recalc_sigpending_tsk(t); - if (signal_pending(t)) - signal_wake_up(t, 0); - } + if (!signal_pending(t) && !(t->flags & PF_EXITING)) + recalc_sigpending_and_wake(t); spin_unlock_irq(&tsk->sighand->siglock); read_unlock(&tasklist_lock); } Index: b/kernel/power/process.c =================================================================== --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -81,7 +81,7 @@ static void cancel_freezing(struct task_ pr_debug(" clean up: %s\n", p->comm); do_not_freeze(p); spin_lock_irqsave(&p->sighand->siglock, flags); - recalc_sigpending_tsk(p); + recalc_sigpending_and_wake(p); spin_unlock_irqrestore(&p->sighand->siglock, flags); } } Index: b/kernel/signal.c =================================================================== --- a/kernel/signal.c +++ b/kernel/signal.c @@ -96,15 +96,27 @@ static inline int has_pending_signals(si #define PENDING(p,b) has_pending_signals(&(p)->signal, (b)) -fastcall void recalc_sigpending_tsk(struct task_struct *t) +static int recalc_sigpending_tsk(struct task_struct *t) { if (t->signal->group_stop_count > 0 || (freezing(t)) || PENDING(&t->pending, &t->blocked) || - PENDING(&t->signal->shared_pending, &t->blocked)) + PENDING(&t->signal->shared_pending, &t->blocked)) { set_tsk_thread_flag(t, TIF_SIGPENDING); - else - clear_tsk_thread_flag(t, TIF_SIGPENDING); + return 1; + } + clear_tsk_thread_flag(t, TIF_SIGPENDING); + return 0; +} + +/* + * After recalculating TIF_SIGPENDING, we need to make sure the task wakes up. + * This is superfluous when called on current, the wakeup is a harmless no-op. + */ +void recalc_sigpending_and_wake(struct task_struct *t) +{ + if (recalc_sigpending_tsk(t)) + signal_wake_up(t, 0); } void recalc_sigpending(void) @@ -703,7 +715,7 @@ force_sig_info(int sig, struct siginfo * action->sa.sa_handler = SIG_DFL; if (blocked) { sigdelset(&t->blocked, sig); - recalc_sigpending_tsk(t); + recalc_sigpending_and_wake(t); } } ret = specific_send_sig_info(sig, info, t); @@ -2254,7 +2266,7 @@ int do_sigaction(int sig, struct k_sigac rm_from_queue_full(&mask, &t->signal->shared_pending); do { rm_from_queue_full(&mask, &t->pending); - recalc_sigpending_tsk(t); + recalc_sigpending_and_wake(t); t = next_thread(t); } while (t != current); }