On 19/08/2022 19:17, Guilherme G. Piccoli wrote:

Commit 8d470a45d1a6 ("panic: add option to dump all CPUs backtraces in panic_print")
introduced a setting for the "panic_print" kernel parameter to allow
users to request a NMI backtrace on panic. Problem is that the panic_print
handling happens after the secondary CPUs are already disabled, hence
this option ended-up being kind of a no-op - kernel skips the NMI trace
in idling CPUs, which is the case of offline CPUs.

Fix it by checking the NMI backtrace bit in the panic_print prior to
the CPU disabling function.

Fixes: 8d470a45d1a6 ("panic: add option to dump all CPUs backtraces in panic_print")
Cc: Feng Tang <redacted>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

---

V3:
- No changes.

V2:
- new patch, there was no V1 of this one.

Hi folks, thanks upfront for reviews. This is a new patch, fixing an issue
I found in my tests, so I shoved it into this fixes series.

Notice that while at it, I got rid of the "crash_kexec_post_notifiers"
local copy in panic(). This was introduced by commit b26e27ddfd2a
("kexec: use core_param for crash_kexec_post_notifiers boot option"),
but it is not clear from comments or commit message why this local copy
is required.

My understanding is that it's a mechanism to prevent some concurrency,
in case some other CPU modify this variable while panic() is running.
I find it very unlikely, hence I removed it - but if people consider
this copy needed, I can respin this patch and keep it, even providing a
comment about that, in order to be explict about its need.

Let me know your thoughts! Cheers,

Guilherme


 kernel/panic.c | 47 +++++++++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 20 deletions(-)
[...]

Hi Andrew, sorry for the ping.

Does the patch makes sense for you? Any comments are much appreciated!
Tnx in advance,


Guilherme