John Stultz hit run_posix_cpu_timers()->BUG_ON(tsk->exit_state), see
http://marc.theaimsgroup.com/?l=linux-kernel&m=115015841413687
This was fixed by
Commit 3de463c7d9d58f8cf3395268230cb20a4c15bffa
[PATCH] posix-timers: remove false BUG_ON() from run_posix_cpu_timers()
(now re-sended as [PATCH 2/3])
but it was reverted because it triggered a problem,
Chris Wright wrote: // Message-ID: <[email protected]>
>
> I'm still getting lockups with current kernel. Let this run for a
> bit, then ^C is typically all it takes. Haven't looked any closer to
> see what's the cause. Looks like deadlock with irq's off, maybe in
> settime vs. run_posix_cpu_timers.
>
> #include <errno.h>
> #include <stdio.h>
> #include <signal.h>
> #include <string.h>
> #include <stdlib.h>
> #include <stdarg.h>
> #include <unistd.h>
> #include <sys/time.h>
> #include <sys/mman.h>
> #include <sched.h>
> #include <pthread.h>
> #include <linux/unistd.h>
>
> #define CPUCLOCK_PERTHREAD_MASK 4
>
> #define MAKE_PROCESS_CPUCLOCK(pid, clock) \
> ((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
>
> #define MAKE_THREAD_CPUCLOCK(tid, clock) \
> MAKE_PROCESS_CPUCLOCK((tid), (clock) | CPUCLOCK_PERTHREAD_MASK)
>
> /* get glibc out of the way */
> static inline int _timer_create(clockid_t c, struct sigevent *e, timer_t *t)
> {
> return syscall(__NR_timer_create, c, e, t);
> }
> static inline int _timer_settime(timer_t t, int f, struct itimerspec *i, struct itimerspec *o)
> {
> return syscall(__NR_timer_settime, t, f, i, o);
> }
>
> int do_thread(void *data)
> {
> struct sigevent sigev = {.sigev_signo = SIGRTMIN,
> .sigev_notify = SIGEV_SIGNAL};
> struct itimerspec itsp = {.it_value.tv_nsec = 1,
> .it_interval.tv_nsec = 1};
> timer_t tid;
> clockid_t clock = MAKE_PROCESS_CPUCLOCK(getpid(), 0);
>
> if (_timer_create(clock, &sigev, &tid) == -1) {
> perror("timer_create");
> syscall(__NR_exit, 1);
> }
>
> if (_timer_settime(tid, 0, &itsp, NULL)) {
> perror("timer_settime");
> syscall(__NR_exit, 1);
> }
> pause();
> syscall(__NR_exit, 0);
> }
>
> int main(int argc, char *argv[])
> {
> int max=(int)(~0U>>1), i=0;
> struct sigaction sa = { .sa_handler = SIG_IGN};
> sigaction(SIGRTMIN, &sa, NULL);
>
> if (argc > 1)
> max = strtoul(argv[1], NULL, 0);
>
> for (i=0; i<max; i++) {
> pid_t tid;
> size_t len = getpagesize();
> void *addr = mmap(NULL, len, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_ANONYMOUS|MAP_GROWSDOWN, -1, 0);
> if (addr == MAP_FAILED) {
> perror("mmap");
> break;
> }
> addr = (void *)((unsigned long)addr + len);
> tid = clone(do_thread, addr,
> SIGCHLD|CLONE_VM|CLONE_SIGHAND|CLONE_FILES|CLONE_THREAD,
> NULL);
> if (tid == -1) {
> perror("clone");
> break;
> }
> }
> printf("maxed %d threads, spinning...\n", i);
> /* eat cpu */
> while(1);
> }
The reason of this lockup is another bug in check_process_timers(),
it may enter an endless loop with ->siglock held, this explains a
trace seen by Chris:
> [ 385.918035] Call Trace: <IRQ> <ffffffff804951c9>{_spin_lock+9} <ffffffff8014eaa4>{arm_timer+116}
> [ 385.927052] <ffffffff8014edc9>{posix_cpu_timer_schedule+265} <ffffffff8014ee39>{cpu_timer_fire+89}
> [ 385.936854] <ffffffff8014fa61>{run_posix_cpu_timers+1761} <ffffffff8014074d>{update_process_times+2}
> [ 385.947008] <ffffffff80119c67>{smp_local_timer_interrupt+183} <ffffffff80119cb9>{smp_apic_timer_int}
> [ 385.957790] <ffffffff8010e9d4>{apic_timer_interrupt+132} <EOI> <ffffffff8049532b>{_spin_unlock_irq}
> [ 385.968051] <ffffffff80143e41>{get_signal_to_deliver+1361} <ffffffff8010d07d>{do_signal+125}
> [ 385.977321] <ffffffff80133ff4>{__put_task_struct+260} <ffffffff80493c50>{thread_return+160}
> [ 385.986499] <ffffffff8014c632>{sys_timer_settime+562} <ffffffff8010dd07>{sysret_signal+28}
> [ 385.995596] <ffffffff8010d7e0>{do_notify_resume+48} <ffffffff8010dfef>{ptregscall_common+103}
This bug is fixed by [PATCH 1/3].
With these patches applied Chris's program exits without any problems.
John, could you please try these patches while you are testing posix
cpu timers?
Oleg.
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