From: Guilherme G. Piccoli gpiccoli@igalia.com
[ 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 christophe.jaillet@wanadoo.fr Cc: Mihai Carabas mihai.carabas@oracle.com Cc: Shile Zhang shile.zhang@linux.alibaba.com Cc: Wang ShaoBo bobo.shaobowang@huawei.com Cc: zhenwei pi pizhenwei@bytedance.com Signed-off-by: Guilherme G. Piccoli gpiccoli@igalia.com Link: https://lore.kernel.org/r/20220427224924.592546-6-gpiccoli@igalia.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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)