From c28739375bf0d6e239b4fa939ec8372aa2c707d2 Mon Sep 17 00:00:00 2001 From: Stanislaw Gruszka Date: Thu, 11 Mar 2010 14:04:42 -0800 Subject: [PATCH] cpu-timers: Avoid iterating over all threads in fastpath_timer_check() Spread p->sighand->siglock locking scope to make sure that fastpath_timer_check() never iterates over all threads. Without locking there is small possibility that signal->cputimer will stop running while we write values to signal->cputime_expires. Calling thread_group_cputime() from fastpath_timer_check() is not only bad because it is slow, also it is racy with __exit_signal() which can lead to invalid signal->{s,u}time values. Signed-off-by: Stanislaw Gruszka Cc: Ingo Molnar Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Hidetoshi Seto Cc: Balbir Singh Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/posix-cpu-timers.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 7d9d0fa..564b3b0 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -550,7 +550,7 @@ static inline int expires_gt(cputime_t expires, cputime_t new_exp) /* * Insert the timer on the appropriate list before any timers that * expire later. This must be called with the tasklist_lock held - * for reading, and interrupts disabled. + * for reading, interrupts disabled and p->sighand->siglock taken. */ static void arm_timer(struct k_itimer *timer) { @@ -569,9 +569,6 @@ static void arm_timer(struct k_itimer *timer) } head += CPUCLOCK_WHICH(timer->it_clock); - BUG_ON(!irqs_disabled()); - spin_lock(&p->sighand->siglock); - listpos = head; list_for_each_entry(next, head, entry) { if (cpu_time_before(timer->it_clock, nt->expires, next->expires)) @@ -606,8 +603,6 @@ static void arm_timer(struct k_itimer *timer) break; } } - - spin_unlock(&p->sighand->siglock); } /* @@ -720,7 +715,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, ret = TIMER_RETRY; } else list_del_init(&timer->it.cpu.entry); - spin_unlock(&p->sighand->siglock); /* * We need to sample the current value to convert the new @@ -774,6 +768,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, * disable this firing since we are already reporting * it as an overrun (thanks to bump_cpu_timer above). */ + spin_unlock(&p->sighand->siglock); read_unlock(&tasklist_lock); goto out; } @@ -793,6 +788,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, arm_timer(timer); } + spin_unlock(&p->sighand->siglock); read_unlock(&tasklist_lock); /* @@ -1206,6 +1202,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) goto out; } read_lock(&tasklist_lock); /* arm_timer needs it. */ + spin_lock(&p->sighand->siglock); } else { read_lock(&tasklist_lock); if (unlikely(p->signal == NULL)) { @@ -1226,6 +1223,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) clear_dead_task(timer, now); goto out_unlock; } + spin_lock(&p->sighand->siglock); cpu_timer_sample_group(timer->it_clock, p, &now); bump_cpu_timer(timer, now); /* Leave the tasklist_lock locked for the call below. */ @@ -1234,7 +1232,9 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) /* * Now re-arm for the new expiry time. */ + BUG_ON(!irqs_disabled()); arm_timer(timer); + spin_unlock(&p->sighand->siglock); out_unlock: read_unlock(&tasklist_lock); -- 2.7.4