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From: Josh Poimboeuf <>
	Peter Zijlstra <>,
	Wang ShaoBo <>
Subject: [PATCH 2/2] x86/stacktrace: Fix reliable check for empty user task stacks
Date: Fri, 17 Jul 2020 09:04:26 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

If a user task's stack is empty, or if it only has user regs, ORC
reports it as a reliable empty stack.  But arch_stack_walk_reliable()
incorrectly treats it as unreliable.

That happens because the only success path for user tasks is inside the
loop, which only iterates on non-empty stacks.  Generally, a user task
must end in a user regs frame, but an empty stack is an exception to
that rule.

Thanks to commit 71c95825289f ("x86/unwind/orc: Fix error handling in
__unwind_start()"), unwind_start() now sets state->error appropriately.
So now for both ORC and FP unwinders, unwind_done() and !unwind_error()
always means the end of the stack was successfully reached.  So the
success path for kthreads is no longer needed -- it can also be used for
empty user tasks.

Reported-by: Wang ShaoBo <>
Signed-off-by: Josh Poimboeuf <>
 arch/x86/kernel/stacktrace.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 6ad43fc44556..2fd698e28e4d 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -58,7 +58,6 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 			 * or a page fault), which can make frame pointers
 			 * unreliable.
 				return -EINVAL;
@@ -81,10 +80,6 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 	if (unwind_error(&state))
 		return -EINVAL;
-	/* Success path for non-user tasks, i.e. kthreads and idle tasks */
-	if (!(task->flags & (PF_KTHREAD | PF_IDLE)))
-		return -EINVAL;
 	return 0;

  parent reply	other threads:[~2020-07-17 14:04 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 14:04 [PATCH 0/2] x86/unwind: A couple of fixes for newly forked tasks Josh Poimboeuf
2020-07-17 14:04 ` [PATCH 1/2] x86/unwind/orc: Fix ORC " Josh Poimboeuf
2020-07-17 14:04 ` Josh Poimboeuf [this message]
2020-07-20 11:06 ` [PATCH 0/2] x86/unwind: A couple of fixes " Wangshaobo (bobo)

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