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| author | Roman Gushchin <guro@fb.com> | 2019-05-16 10:38:21 -0700 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2019-05-16 10:43:58 -0700 |
| commit | 05b289263772b0698589abc47771264a685cd365 (patch) | |
| tree | f892ca93254af2d0ba4688b26528cadb705d2661 /kernel/signal.c | |
| parent | 8c05f3b965da14e7790711026b32cc10a4c06213 (diff) | |
| download | linux-05b289263772b0698589abc47771264a685cd365.tar.bz2 | |
signal: unconditionally leave the frozen state in ptrace_stop()
Alex Xu reported a regression in strace, caused by the introduction of
the cgroup v2 freezer. The regression can be reproduced by stracing
the following simple program:
#include <unistd.h>
int main() {
write(1, "a", 1);
return 0;
}
An attempt to run strace ./a.out leads to the infinite loop:
[ pre-main omitted ]
write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
write(1, "a", 1) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
[ repeats forever ]
The problem occurs because the traced task leaves ptrace_stop()
(and the signal handling loop) with the frozen bit set. So let's
call cgroup_leave_frozen(true) unconditionally after sleeping
in ptrace_stop().
With this patch applied, strace works as expected:
[ pre-main omitted ]
write(1, "a", 1) = 1
exit_group(0) = ?
+++ exited with 0 +++
Reported-by: Alex Xu <alex_y_xu@yahoo.ca>
Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/signal.c')
| -rw-r--r-- | kernel/signal.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index c4dd66436fc5..a1eb44dc9ff5 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2113,6 +2113,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t preempt_enable_no_resched(); cgroup_enter_frozen(); freezable_schedule(); + cgroup_leave_frozen(true); } else { /* * By the time we got the lock, our tracer went away. |