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2006-10-17[PATCH] posix-cpu-timers: prevent signal delivery starvationThomas Gleixner
The integer divisions in the timer accounting code can round the result down to 0. Adding 0 is without effect and the signal delivery stops. Clamp the division result to minimum 1 to avoid this. Problem was reported by Seongbae Park <spark@google.com>, who provided also an inital patch. Roland sayeth: I have had some more time to think about the problem, and to reproduce it using Toyo's test case. For the record, if my understanding of the problem is correct, this happens only in one very particular case. First, the expiry time has to be so soon that in cputime_t units (usually 1s/HZ ticks) it's < nthreads so the division yields zero. Second, it only affects each thread that is so new that its CPU time accumulation is zero so now+0 is still zero and ->it_*_expires winds up staying zero. For the VIRT and PROF clocks when cputime_t is tick granularity (or the SCHED clock on configurations where sched_clock's value only advances on clock ticks), this is not hard to arrange with new threads starting up and blocking before they accumulate a whole tick of CPU time. That's what happens in Toyo's test case. Note that in general it is fine for that division to round down to zero, and set each thread's expiry time to its "now" time. The problem only arises with thread's whose "now" value is still zero, so that now+0 winds up 0 and is interpreted as "not set" instead of ">= now". So it would be a sufficient and more precise fix to just use max(ticks, 1) inside the loop when setting each it_*_expires value. But, it does no harm to round the division up to one and always advance every thread's expiry time. If the thread didn't already fire timers for the expiry time of "now", there is no expectation that it will do so before the next tick anyway. So I followed Thomas's patch in lifting the max out of the loops. This patch also covers the reload cases, which are harder to write a test for (and I didn't try). I've tested it with Toyo's case and it fixes that. [toyoa@mvista.com: fix: min_t -> max_t] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Roland McGrath <roland@redhat.com> Cc: Daniel Walker <dwalker@mvista.com> Cc: Toyo Abe <toyoa@mvista.com> Cc: john stultz <johnstul@us.ibm.com> Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Seongbae Park <spark@google.com> Cc: Peter Mattis <pmattis@google.com> Cc: Rohit Seth <rohitseth@google.com> Cc: Martin Bligh <mbligh@google.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-09-29[PATCH] posix-timers: Fix the flags handling in posix_cpu_nsleep()Toyo Abe
When a posix_cpu_nsleep() sleep is interrupted by a signal more than twice, it incorrectly reports the sleep time remaining to the user. Because posix_cpu_nsleep() doesn't report back to the user when it's called from restart function due to the wrong flags handling. This patch, which applies after previous one, moves the nanosleep() function from posix_cpu_nsleep() to do_cpu_nanosleep() and cleans up the flags handling appropriately. Signed-off-by: Toyo Abe <toyoa@mvista.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-09-29[PATCH] posix-timers: Fix clock_nanosleep() doesn't return the remaining ↵Toyo Abe
time in compatibility mode The clock_nanosleep() function does not return the time remaining when the sleep is interrupted by a signal. This patch creates a new call out, compat_clock_nanosleep_restart(), which handles returning the remaining time after a sleep is interrupted. This patch revives clock_nanosleep_restart(). It is now accessed via the new call out. The compat_clock_nanosleep_restart() is used for compatibility access. Since this is implemented in compatibility mode the normal path is virtually unaffected - no real performance impact. Signed-off-by: Toyo Abe <toyoa@mvista.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17[PATCH] arm_timer: remove a racy and obsolete PF_EXITING checkOleg Nesterov
arm_timer() checks PF_EXITING to prevent BUG_ON(->exit_state) in run_posix_cpu_timers(). However, for some reason it does so only for CPUCLOCK_PERTHREAD case (which is imho wrong). Also, this check is not reliable, PF_EXITING could be set on another cpu without any locks/barriers just after the check, so it can't prevent from attaching the timer to the exiting task. The previous patch makes this check unneeded. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17[PATCH] run_posix_cpu_timers: remove a bogus BUG_ON()Oleg Nesterov
do_exit() clears ->it_##clock##_expires, but nothing prevents another cpu to attach the timer to exiting process after that. arm_timer() tries to protect against this race, but the check is racy. After exit_notify() does 'write_unlock_irq(&tasklist_lock)' and before do_exit() calls 'schedule() local timer interrupt can find tsk->exit_state != 0. If that state was EXIT_DEAD (or another cpu does sys_wait4) interrupted task has ->signal == NULL. At this moment exiting task has no pending cpu timers, they were cleanuped in __exit_signal()->posix_cpu_timers_exit{,_group}(), so we can just return from irq. John Stultz recently confirmed this bug, see http://marc.theaimsgroup.com/?l=linux-kernel&m=115015841413687 Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-17[PATCH] check_process_timers: fix possible lockupOleg Nesterov
If the local timer interrupt happens just after do_exit() sets PF_EXITING (and before it clears ->it_xxx_expires) run_posix_cpu_timers() will call check_process_timers() with tasklist_lock + ->siglock held and check_process_timers: t = tsk; do { .... do { t = next_thread(t); } while (unlikely(t->flags & PF_EXITING)); } while (t != tsk); the outer loop will never stop. Actually, the window is bigger. Another process can attach the timer after ->it_xxx_expires was cleared (see the next commit) and the 'if (PF_EXITING)' check in arm_timer() is racy (see the one after that). Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-10[PATCH] hrtimer: switch clock_nanosleep to hrtimer nanosleep APIThomas Gleixner
Switch clock_nanosleep to use the new nanosleep functions in hrtimer.c Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-10[PATCH] hrtimer: make clockid_t arguments constThomas Gleixner
add const arguments to the posix-timers.h API functions Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-06[PATCH] Fix posix-cpu-timers sched_time accumulationDavid S. Miller
I've spent the past 3 days digging into a glibc testsuite failure in current CVS, specifically libc/rt/tst-cputimer1.c The thr1 and thr2 timers fire too early in the second pass of this test. The second pass is noteworthy because it makes use of intervals, whereas the first pass does not. All throughout the posix-cpu-timers.c code, the calculation of the process sched_time sum is implemented roughly as: unsigned long long sum; sum = tsk->signal->sched_time; t = tsk; do { sum += t->sched_time; t = next_thread(t); } while (t != tsk); In fact this is the exact scheme used by check_process_timers(). In the case of check_process_timers(), current->sched_time has just been updated (via scheduler_tick(), which is invoked by update_process_times(), which subsequently invokes run_posix_cpu_timers()) So there is no special processing necessary wrt. that. In other contexts, we have to allot for the fact that tsk->sched_time might be a bit out of date if we are current. And the posix-cpu-timers.c code uses current_sched_time() to deal with that. Unfortunately it does so in an erroneous and inconsistent manner in one spot which is what results in the early timer firing. In cpu_clock_sample_group_locked(), it does this: cpu->sched = p->signal->sched_time; /* Add in each other live thread. */ while ((t = next_thread(t)) != p) { cpu->sched += t->sched_time; } if (p->tgid == current->tgid) { /* * We're sampling ourselves, so include the * cycles not yet banked. We still omit * other threads running on other CPUs, * so the total can always be behind as * much as max(nthreads-1,ncpus) * (NSEC_PER_SEC/HZ). */ cpu->sched += current_sched_time(current); } else { cpu->sched += p->sched_time; } The problem is the "p->tgid == current->tgid" test. If "p" is not current, and the tgids are the same, we will add the process t->sched_time twice into cpu->sched and omit "p"'s sched_time which is very very very wrong. posix-cpu-timers.c has a helper function, sched_ns(p) which takes care of this, so my fix is to use that here instead of this special tgid test. The fact that current can be one of the sub-threads of "p" points out that we could make things a little bit more accurate, perhaps by using sched_ns() on every thread we process in these loops. It also points out that we don't use the most accurate value for threads in the group actively running other cpus (and this is mentioned in the comment). But that is a future enhancement, and this fix here definitely makes sense. Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-11-28[PATCH] fix 32bit overflow in timespec_to_sample()Oleg Nesterov
fix 32bit overflow in timespec_to_sample() Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-11-07[PATCH] posix-timers `unlikely' rejigAndrew Morton
!unlikely(expr) hurts my brain. likely(!expr) is more straightforward. Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-30[PATCH] posix-cpu-timers: fix overrun reportingRoland McGrath
This change corrects an omission in posix_cpu_timer_schedule, so that it correctly propagates the overrun calculation to where it will get reported to the user. Signed-off-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-27[PATCH] Yet more posix-cpu-timer fixesRoland McGrath
This just makes sure that a thread's expiry times can't get reset after it clears them in do_exit. This is what allowed us to re-introduce the stricter BUG_ON() check in a362f463a6d316d14daed0f817e151835ce97ff7. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-27Revert "remove false BUG_ON() from run_posix_cpu_timers()"Linus Torvalds
This reverts commit 3de463c7d9d58f8cf3395268230cb20a4c15bffa. Roland has another patch that allows us to leave the BUG_ON() in place by just making sure that the condition it tests for really is always true. That goes in next. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-26[PATCH] Fix cpu timers expiration timeOleg Nesterov
There's a silly off-by-one error in the code that updates the expiration of posix CPU timers, causing them to not be properly updated when they hit exactly on their expiration time (which should be the normal case). This causes them to then fire immediately again, and only _then_ get properly updated. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-26posix cpu timers: fix timer orderingLinus Torvalds
Pointed out by Oleg Nesterov, who has been walking over the code forwards and backwards. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-24[PATCH] posix-timers: fix posix_cpu_timer_set() vs run_posix_cpu_timers() raceOleg Nesterov
This might be harmless, but looks like a race from code inspection (I was unable to trigger it). I must admit, I don't understand why we can't return TIMER_RETRY after 'spin_unlock(&p->sighand->siglock)' without doing bump_cpu_timer(), but this is what original code does. posix_cpu_timer_set: read_lock(&tasklist_lock); spin_lock(&p->sighand->siglock); list_del_init(&timer->it.cpu.entry); spin_unlock(&p->sighand->siglock); We are probaly deleting the timer from run_posix_cpu_timers's 'firing' local list_head while run_posix_cpu_timers() does list_for_each_safe. Various bad things can happen, for example we can just delete this timer so that list_for_each() will not notice it and run_posix_cpu_timers() will not reset '->firing' flag. In that case, .... if (timer->it.cpu.firing) { read_unlock(&tasklist_lock); timer->it.cpu.firing = -1; return TIMER_RETRY; } sys_timer_settime() goes to 'retry:', calls posix_cpu_timer_set() again, it returns TIMER_RETRY ... Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-24[PATCH] posix-timers: exit path cleanupOleg Nesterov
No need to rebalance when task exited Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-24[PATCH] posix-timers: remove false BUG_ON() from run_posix_cpu_timers()Oleg Nesterov
do_exit() clears ->it_##clock##_expires, but nothing prevents another cpu to attach the timer to exiting process after that. After exit_notify() does 'write_unlock_irq(&tasklist_lock)' and before do_exit() calls 'schedule() local timer interrupt can find tsk->exit_state != 0. If that state was EXIT_DEAD (or another cpu does sys_wait4) interrupted task has ->signal == NULL. At this moment exiting task has no pending cpu timers, they were cleaned up in __exit_signal()->posix_cpu_timers_exit{,_group}(), so we can just return from irq. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-24[PATCH] posix-timers: fix cleanup_timers() and run_posix_cpu_timers() racesOleg Nesterov
1. cleanup_timers() sets timer->task = NULL under tasklist + ->sighand locks. That means that this code in posix_cpu_timer_del() and posix_cpu_timer_set() lock_timer(timer); if (timer->task == NULL) return; read_lock(tasklist); put_task_struct(timer->task) is racy. With this patch timer->task modified and accounted only under timer->it_lock. Sadly, this means that dead task_struct won't be freed until timer deleted or armed. 2. run_posix_cpu_timers() collects expired timers into local list under tasklist + ->sighand again. That means that posix_cpu_timer_del() should check timer->it.cpu.firing under these locks too. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-23Posix timers: limit number of timers firing at onceLinus Torvalds
Bursty timers aren't good for anybody, very much including latency for other programs when we trigger lots of timers in interrupt context. So set a random limit, after which we'll handle the rest on the next timer tick. Noted by Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-21Revert "Fix cpu timers exit deadlock and races"Linus Torvalds
Revert commit e03d13e985d48ac4885382c9e3b1510c78bd047f, to be replaced by a much nicer fix from Roland.
2005-10-19[PATCH] Fix cpu timers exit deadlock and racesRoland McGrath
Oleg Nesterov reported an SMP deadlock. If there is a running timer tracking a different process's CPU time clock when the process owning the timer exits, we deadlock on tasklist_lock in posix_cpu_timer_del via exit_itimers. That code was using tasklist_lock to check for a race with __exit_signal being called on the timer-target task and clearing its ->signal. However, there is actually no such race. __exit_signal will have called posix_cpu_timers_exit and posix_cpu_timers_exit_group before it does that. Those will clear those k_itimer's association with the dying task, so posix_cpu_timer_del will return early and never reach the code in question. In addition, posix_cpu_timer_del called from exit_itimers during execve or directly from timer_delete in the process owning the timer can race with an exiting timer-target task to cause a double put on timer-target task struct. Make sure we always access cpu_timers lists with sighand lock held. Signed-off-by: Roland McGrath <roland@redhat.com> Signed-off-by: Chris Wright <chrisw@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-17[PATCH] posix-timers: fix task accountingOleg Nesterov
Make sure we release the task struct properly when releasing pending timers. release_task() does write_lock_irq(&tasklist_lock), so it can't race with run_posix_cpu_timers() on any cpu. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-04-16Linux-2.6.12-rc2Linus Torvalds
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!