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ptrace: make wait_on_bit(JOBCTL_TRAPPING_BIT) in ptrace_attach() killable

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ptrace_attach() can hang waiting for STOPPED -> TRACED transition if the
tracee gets frozen in between, change wait_on_bit() to use TASK_KILLABLE.

This doesn't really solve the problem(s) and we probably need to fix the
freezer.  In particular, note that this means that pm freezer will fail if
it races attach-to-stopped-task.

And otoh perhaps we can just remove JOBCTL_TRAPPING_BIT altogether, it is
not clear if we really need to hide this transition from debugger, WNOHANG
after PTRACE_ATTACH can fail anyway if it races with SIGCONT.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Roland McGrath <roland@hack.frob.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Pedro Alves <palves@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2016-01-20 14:59:55 -08:00 committed by Linus Torvalds
parent 8992de4cec
commit 7c3b00e06d
1 changed files with 8 additions and 2 deletions
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10
kernel/ptrace.c
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@ -364,8 +364,14 @@ static int ptrace_attach(struct task_struct *task, long request,
mutex_unlock(&task->signal->cred_guard_mutex);
out:
if (!retval) {
wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT,
TASK_UNINTERRUPTIBLE);
/*
* We do not bother to change retval or clear JOBCTL_TRAPPING
* if wait_on_bit() was interrupted by SIGKILL. The tracer will
* not return to user-mode, it will exit and clear this bit in
* __ptrace_unlink() if it wasn't already cleared by the tracee;
* and until then nobody can ptrace this task.
*/
wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT, TASK_KILLABLE);
proc_ptrace_connector(task, PTRACE_ATTACH);
}