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x86/stacktrace: Fix reliable check for empty user task stacks 

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 71c9582528 ("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 <bobo.shaobowang@huawei.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Link: https://lkml.kernel.org/r/f136a4e5f019219cbc4f4da33b30c2f44fa65b84.1594994374.git.jpoimboe@redhat.com
zero-sugar-mainline-defconfig
Josh Poimboeuf 2020-07-17 09:04:26 -05:00 committed by Thomas Gleixner
parent 372a8eaa05
commit 039a7a30ec
1 changed files with 0 additions and 5 deletions
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5
arch/x86/kernel/stacktrace.c
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@ -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.
*/
if (IS_ENABLED(CONFIG_FRAME_POINTER))
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;
}