Messages in this thread Patch in this message | | | From | "Guilherme G. Piccoli" <> | Subject | [PATCH V3] firmware: google: Test spinlock on panic path to avoid lockups | Date | Fri, 19 Aug 2022 12:50:59 -0300 |
| |
Currently the gsmi driver registers a panic notifier as well as reboot and die notifiers. The callbacks registered are called in atomic and very limited context - for instance, panic disables preemption and local IRQs, also all secondary CPUs (not executing the panic path) are shutdown.
With that said, taking a spinlock in this scenario is a dangerous invitation for lockup scenarios. So, fix that by checking if the spinlock is free to acquire in the panic notifier callback - if not, bail-out and avoid a potential hang.
Fixes: 74c5b31c6618 ("driver: Google EFI SMI") Cc: Ard Biesheuvel <ardb@kernel.org> Cc: David Gow <davidgow@google.com> Cc: Julius Werner <jwerner@chromium.org> Reviewed-by: Evan Green <evgreen@chromium.org> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> ---
This is a re-submission of the patch - it was in a series [0], but Greg suggested me to resubmit individually in order it gets picked by the relevant maintainers, instead of asking them to merge individual patches from a series. Notice I've trimmed a bit the CC list, it was bigger due to the patch being in a series...
This is truly the V3 of the patch, below is the diff between versions:
V3: - added Evan's review tag - thanks!
V2: - do not use spin_trylock anymore, to avoid messing with non-panic paths; now we just check the spinlock state in the panic notifier before taking it. Thanks Evan for the review!
[0] https://lore.kernel.org/lkml/20220719195325.402745-4-gpiccoli@igalia.com/
drivers/firmware/google/gsmi.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c index adaa492c3d2d..3ef5f3c0b4e4 100644 --- a/drivers/firmware/google/gsmi.c +++ b/drivers/firmware/google/gsmi.c @@ -681,6 +681,14 @@ static struct notifier_block gsmi_die_notifier = { static int gsmi_panic_callback(struct notifier_block *nb, unsigned long reason, void *arg) { + /* + * Perform the lock check before effectively trying + * to acquire it on gsmi_shutdown_reason() to avoid + * potential lockups in atomic context. + */ + if (spin_is_locked(&gsmi_dev.lock)) + return NOTIFY_DONE; + gsmi_shutdown_reason(GSMI_SHUTDOWN_PANIC); return NOTIFY_DONE; } -- 2.37.2
| |