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Oleg Nesterov 788e05a67c [PATCH] fix do_coredump() vs SIGSTOP race ... Let's suppose we have 2 threads in thread group: A - does coredump B - has pending SIGSTOP thread A thread B do_coredump: get_signal_to_deliver: lock(->sighand) ->signal->flags = SIGNAL_GROUP_EXIT unlock(->sighand) lock(->sighand) signr = dequeue_signal() ->signal->flags |= SIGNAL_STOP_DEQUEUED return SIGSTOP; do_signal_stop: unlock(->sighand) coredump_wait: zap_threads: lock(tasklist_lock) send SIGKILL to B // signal_wake_up() does nothing unlock(tasklist_lock) lock(tasklist_lock) lock(->sighand) re-check sig->flags & SIGNAL_STOP_DEQUEUED, yes set_current_state(TASK_STOPPED); finish_stop: schedule(); // ->state == TASK_STOPPED wait_for_completion(&startup_done) // waits for complete() from B, // ->state == TASK_UNINTERRUPTIBLE We can't wake up 'B' in any way: SIGCONT will be ignored because handle_stop_signal() sees ->signal->flags & SIGNAL_GROUP_EXIT. sys_kill(SIGKILL)->__group_complete_signal() will choose uninterruptible 'A', so it can't help. sys_tkill(B, SIGKILL) will be ignored by specific_send_sig_info() because B already has pending SIGKILL. This scenario is not possbile if 'A' does do_group_exit(), because it sets sig->flags = SIGNAL_GROUP_EXIT and delivers SIGKILL to subthreads atomically, holding both tasklist_lock and sighand->lock. That means that do_signal_stop() will notice !SIGNAL_STOP_DEQUEUED after re-locking ->sighand. And it is not possible to any other thread to re-add SIGNAL_STOP_DEQUEUED later, because dequeue_signal() can only return SIGKILL. I think it is better to change do_coredump() to do sigaddset(SIGKILL) and signal_wake_up() under sighand->lock, but this patch is much simpler. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Linus Torvalds <torvalds@osdl.org>		19 years ago
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irq	…
power	[PATCH] swsusp: avoid problems if there are too many pages to save	20 years ago
Kconfig.hz	[PATCH] i386: Selectable Frequency of the Timer Interrupt	20 years ago
Kconfig.preempt	…
Makefile	…
acct.c	[PATCH] kernel/acct: add kerneldoc	20 years ago
audit.c	Merge master.kernel.org:/pub/scm/linux/kernel/git/dwmw2/audit-2.6	20 years ago
auditsc.c	…
capability.c	…
compat.c	[PATCH] kernel: fix-up schedule_timeout() usage	20 years ago
configs.c	…
cpu.c	…
cpuset.c	…
crash_dump.c	…
dma.c	…
exec_domain.c	…
exit.c	…
extable.c	…
fork.c	…
futex.c	…
intermodule.c	…
itimer.c	[PATCH] itimer fixes	20 years ago
kallsyms.c	…
kexec.c	…
kfifo.c	…
kmod.c	…
kprobes.c	…
ksysfs.c	…
kthread.c	…
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params.c	…
pid.c	…
posix-cpu-timers.c	…
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printk.c	…
profile.c	…
ptrace.c	…
rcupdate.c	[PATCH] files: rcuref APIs	20 years ago
resource.c	…
sched.c	…
seccomp.c	…
signal.c	[PATCH] fix do_coredump() vs SIGSTOP race	19 years ago
softirq.c	…
softlockup.c	…
spinlock.c	…
stop_machine.c	…
sys.c	[PATCH] reboot: comment and factor the main reboot functions	20 years ago
sys_ni.c	[PATCH] remove sys_set_zone_reclaim()	20 years ago
sysctl.c	[NET]: Fix sparse warnings	20 years ago
time.c	…
timer.c	…
uid16.c	…
user.c	…
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