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authorRoman Gushchin <guro@fb.com>2019-05-16 10:38:21 -0700
committerTejun Heo <tj@kernel.org>2019-05-16 10:43:58 -0700
commit05b289263772b0698589abc47771264a685cd365 (patch)
treef892ca93254af2d0ba4688b26528cadb705d2661 /kernel
parent8c05f3b965da14e7790711026b32cc10a4c06213 (diff)
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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')
-rw-r--r--kernel/signal.c1
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.