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519fb5c335
Dave Jones and Steven Rostedt reported unwinder warnings like the
following:
WARNING: kernel stack frame pointer at ffff8800bda0ff30 in sshd:1090 has bad value 000055b32abf1fa8
In both cases, the unwinder was attempting to unwind from an ftrace
handler into entry code. The callchain was something like:
syscall entry code
C function
ftrace handler
save_stack_trace()
The problem is that the unwinder's end-of-stack logic gets confused by
the way ftrace lays out the stack frame (with fentry enabled).
I was able to recreate this warning with:
echo call_usermodehelper_exec_async:stacktrace > /sys/kernel/debug/tracing/set_ftrace_filter
(exit login session)
I considered fixing this by changing the ftrace code to rewrite the
stack to make the unwinder happy. But that seemed too intrusive after I
implemented it. Instead, just add another check to the unwinder's
end-of-stack logic to detect this special case.
Side note: We could probably get rid of these end-of-stack checks by
encoding the frame pointer for syscall entry just like we do for
interrupt entry. That would be simpler, but it would also be a lot more
intrusive since it would slightly affect the performance of every
syscall.
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: live-patching@vger.kernel.org
Fixes:
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| .. | ||
| alpha | ||
| arc | ||
| arm | ||
| arm64 | ||
| blackfin | ||
| c6x | ||
| cris | ||
| frv | ||
| h8300 | ||
| hexagon | ||
| ia64 | ||
| m32r | ||
| m68k | ||
| metag | ||
| microblaze | ||
| mips | ||
| mn10300 | ||
| nios2 | ||
| openrisc | ||
| parisc | ||
| powerpc | ||
| s390 | ||
| score | ||
| sh | ||
| sparc | ||
| tile | ||
| um | ||
| unicore32 | ||
| x86 | ||
| xtensa | ||
| .gitignore | ||
| Kconfig | ||