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misc/pvpanic: Convert regular spinlock into trylock on panic path 

[ Upstream commit e918c10265 ]

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 b3c0f87746 ("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: b3c0f87746 ("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>
This commit is contained in:
Guilherme G. Piccoli 2022-04-27 19:48:59 -03:00 committed by Greg Kroah-Hartman
parent 19fc743bb2
commit 054d5cdeb0
1 changed files with 8 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
drivers/misc/pvpanic/pvpanic.c
View File

@ -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);
@ -55,9 +57,13 @@ pvpanic_panic_notify(struct notifier_block *nb, unsigned long code, void *unused
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)