Attachment 185931 Details for Bug 248532 – Roland's fix for the Comment 12 testcase.

[patch] Roland's fix for the Comment 12 testcase.

bz248532c13.patch (text/plain), 3.35 KB, created by Jan Kratochvil on 2007-09-04 09:16:31 UTC

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Creator: Jan Kratochvil

Created: 2007-09-04 09:16:31 UTC

Size: 3.35 KB

patch

obsolete

>From 4e59f8ca921d3656fd2b344a3bccc3dac5bce0bf Mon Sep 17 00:00:00 2001
>From: Roland McGrath <roland@redhat.com>
>Date: Tue, 4 Sep 2007 01:57:34 -0700
>Subject: [PATCH] Fix ptrace_do_wait race with SIGCONT wakeup
>
>This fixes ptrace_do_wait to distinguish ptrace stops from job control
>stops and never report as stopped a task that's neither in a ptrace stop
>nor in TASK_STOPPED state.  Previously, a ptrace'd task in TASK_RUNNING
>could be reported as stopped when SIGCONT had just woken it (but it had not
>yet cleared its ->exit_code).
>
>Signed-off-by: Roland McGrath <roland@redhat.com>
>---
> kernel/ptrace.c |   41 +++++++++++++++++++++++++++++++++++++++--
> 1 files changed, 39 insertions(+), 2 deletions(-)
>
>diff --git a/kernel/ptrace.c b/kernel/ptrace.c
>index 99f2c68..d4fda84 100644
>--- a/kernel/ptrace.c
>+++ b/kernel/ptrace.c
>@@ -79,6 +79,14 @@ struct ptrace_state
> 
> static const struct utrace_engine_ops ptrace_utrace_ops; /* Initialized below. */
> 
>+/*
>+ * We use this bit in task_struct.exit_code of a ptrace'd task to indicate
>+ * a ptrace stop.  It must not overlap with any bits used in real exit_code's.
>+ * Those are (PTRACE_EVENT_* << 8) | 0xff.
>+ */
>+#define PTRACE_TRAPPED_MASK	0x10000
>+
>+
> static void
> ptrace_state_unlink(struct ptrace_state *state)
> {
>@@ -1292,7 +1300,29 @@ ptrace_do_wait(struct task_struct *tsk,
> 		 * check fails we are sure to get a wakeup if it stops.
> 		 */
> 		exit_code = xchg(&p->exit_code, 0);
>-		if (exit_code)
>+		if (exit_code & PTRACE_TRAPPED_MASK)
>+			goto found;
>+
>+		/*
>+		 * If p was in job-control stop (TASK_STOPPED) rather than
>+		 * ptrace stop (TASK_TRACED), then SIGCONT can asynchronously
>+		 * clear it back to TASK_RUNNING.  Until it gets scheduled
>+		 * and clears its own ->exit_code, our xchg below will see
>+		 * its stop signal.  But, we must not report it if it's no
>+		 * longer in TASK_STOPPED, as vanilla wait would not--the
>+		 * caller can tell if it sent the SIGCONT before calling
>+		 * wait.  We must somehow distinguish this from the case
>+		 * where p is in TASK_RUNNING with p->exit_code set because
>+		 * it is on its way to entering TASK_TRACED (QUIESCE) for our
>+		 * stop.  So, ptrace_report sets the PTRACE_TRAPPED_MASK bit
>+		 * in exit_code when it's setting QUIESCE.  For a job control
>+		 * control stop, that bit will never have been set.  Since
>+		 * the bit's not set now, we should only report right now if
>+		 * p is still stopped.  For this case we are protected by
>+		 * races the same wait that vanilla do_wait (exit.c) is:
>+		 * wait_chldexit is woken after p->state is set to TASK_STOPPED.
>+		 */
>+		if (p->state == TASK_STOPPED)
> 			goto found;
> 
> 		// XXX should handle WCONTINUED
>@@ -1343,6 +1373,7 @@ found:
> 	}
> 	else {
> 		why = CLD_TRAPPED;
>+		exit_code &= ~PTRACE_TRAPPED_MASK;
> 		status = exit_code;
> 		exit_code = (status << 8) | 0x7f;
> 	}
>@@ -1510,8 +1541,14 @@ ptrace_report(struct utrace_attached_engine *engine,
> 	 */
> 	utrace_set_flags(tsk, engine, engine->flags | UTRACE_ACTION_QUIESCE);
> 
>+	/*
>+	 * The PTRACE_TRAPPED_MASK bit distinguishes to ptrace_do_wait that
>+	 * this is a ptrace report, so we expect to enter TASK_TRACED but
>+	 * might not be there yet when examined.
>+	 */
> 	BUG_ON(code == 0);
>-	tsk->exit_code = code;
>+	WARN_ON(code &~ 0x7ff);
>+	tsk->exit_code = code | PTRACE_TRAPPED_MASK;
> 	do_notify(tsk, state->parent, CLD_TRAPPED);
> 
> 	pr_debug("%d ptrace_report quiescing exit_code %x\n",
>-- 
>1.5.2.4

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