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: 76f969e8 ("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>
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