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authorOleg Nesterov <oleg@redhat.com>2016-01-20 14:59:55 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-20 17:09:18 -0800
commit7c3b00e06d731a28fc3d17ed02ba250642b15b81 (patch)
treea6367f3ebe8e98bd217336af1f70115ffef5a8b7 /kernel/ptrace.c
parent8992de4cec126c6703ece0747239d071dbce725f (diff)
ptrace: make wait_on_bit(JOBCTL_TRAPPING_BIT) in ptrace_attach() killable
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>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index b760bae64cf1..aa94aee9d4c9 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -364,8 +364,14 @@ unlock_creds:
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);
}