From ede2512937539b5f7042be8e6a5fd570c066f5e7 Mon Sep 17 00:00:00 2001 From: "Guilherme G. Piccoli" Date: Wed, 27 Apr 2022 19:48:59 -0300 Subject: [PATCH] misc/pvpanic: Convert regular spinlock into trylock on panic path [ Upstream commit e918c10265ef2bc82ce8a6fed6d8123d09ec1db3 ] The pvpanic driver relies on panic notifiers to execute a callback on panic event. Such function is executed in atomic context - the panic function disables local IRQs, preemption and all other CPUs that aren't running the panic code. With that said, it's dangerous to use regular spinlocks in such path, as introduced by commit b3c0f8774668 ("misc/pvpanic: probe multiple instances"). This patch fixes that by replacing regular spinlocks with the trylock safer approach. It also fixes an old comment (about a long gone framebuffer code) and the notifier priority - we should execute hypervisor notifiers early, deferring this way the panic action to the hypervisor, as expected by the users that are setting up pvpanic. Fixes: b3c0f8774668 ("misc/pvpanic: probe multiple instances") Cc: Christophe JAILLET Cc: Mihai Carabas Cc: Shile Zhang Cc: Wang ShaoBo Cc: zhenwei pi Signed-off-by: Guilherme G. Piccoli Link: https://lore.kernel.org/r/20220427224924.592546-6-gpiccoli@igalia.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/misc/pvpanic/pvpanic.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/misc/pvpanic/pvpanic.c b/drivers/misc/pvpanic/pvpanic.c index 700d7d02c800..b9e6400a574b 100644 --- a/drivers/misc/pvpanic/pvpanic.c +++ b/drivers/misc/pvpanic/pvpanic.c @@ -34,7 +34,9 @@ pvpanic_send_event(unsigned int event) { struct pvpanic_instance *pi_cur; - spin_lock(&pvpanic_lock); + if (!spin_trylock(&pvpanic_lock)) + return; + list_for_each_entry(pi_cur, &pvpanic_list, list) { if (event & pi_cur->capability & pi_cur->events) iowrite8(event, pi_cur->base); @@ -56,9 +58,13 @@ pvpanic_panic_notify(struct notifier_block *nb, unsigned long code, return NOTIFY_DONE; } +/* + * Call our notifier very early on panic, deferring the + * action taken to the hypervisor. + */ static struct notifier_block pvpanic_panic_nb = { .notifier_call = pvpanic_panic_notify, - .priority = 1, /* let this called before broken drm_fb_helper() */ + .priority = INT_MAX, }; static void pvpanic_remove(void *param)