The patch titled
Subject: ptrace: make wait_on_bit(JOBCTL_TRAPPING_BIT) in ptrace_attach() killable
has been added to the -mm tree. Its filename is
ptrace-make-wait_on_bitjobctl_trapping_bit-in-ptrace_attach-killable.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ptrace-make-wait_on_bitjobctl_trapping_bit-in-ptrace_attach-killable.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ptrace-make-wait_on_bitjobctl_trapping_bit-in-ptrace_attach-killable.patch
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Reported-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Pedro Alves <palves@xxxxxxxxxx>
Cc: Jan Kratochvil <jan.kratochvil@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/ptrace.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff -puN kernel/ptrace.c~ptrace-make-wait_on_bitjobctl_trapping_bit-in-ptrace_attach-killable kernel/ptrace.c
--- a/kernel/ptrace.c~ptrace-make-wait_on_bitjobctl_trapping_bit-in-ptrace_attach-killable
+++ a/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);
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
ptrace-make-wait_on_bitjobctl_trapping_bit-in-ptrace_attach-killable.patch
ptrace-task_stopped_codeptrace-=-true-cant-see-task_stopped-task.patch
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