From: Mainak Sen <msen@nvidia.com>
Date: Mon, 7 Jul 2025 09:17:39 +0000 (+0900)
Subject: gpu: host1x: Fix race in syncpt alloc/free
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c7d393267c497502fa737607f435f05dfe6e3d9b;p=thirdparty%2Fkernel%2Flinux.git

gpu: host1x: Fix race in syncpt alloc/free

Fix race condition between host1x_syncpt_alloc()
and host1x_syncpt_put() by using kref_put_mutex()
instead of kref_put() + manual mutex locking.

This ensures no thread can acquire the
syncpt_mutex after the refcount drops to zero
but before syncpt_release acquires it.
This prevents races where syncpoints could
be allocated while still being cleaned up
from a previous release.

Remove explicit mutex locking in syncpt_release
as kref_put_mutex() handles this atomically.

Signed-off-by: Mainak Sen <msen@nvidia.com>
Fixes: f5ba33fb9690 ("gpu: host1x: Reserve VBLANK syncpoints at initialization")
Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20250707-host1x-syncpt-race-fix-v1-1-28b0776e70bc@nvidia.com
---

diff --git a/drivers/gpu/host1x/syncpt.c b/drivers/gpu/host1x/syncpt.c
index f63d14a57a1d9..acc7d82e0585e 100644
--- a/drivers/gpu/host1x/syncpt.c
+++ b/drivers/gpu/host1x/syncpt.c
@@ -345,8 +345,6 @@ static void syncpt_release(struct kref *ref)
 
 	sp->locked = false;
 
-	mutex_lock(&sp->host->syncpt_mutex);
-
 	host1x_syncpt_base_free(sp->base);
 	kfree(sp->name);
 	sp->base = NULL;
@@ -369,7 +367,7 @@ void host1x_syncpt_put(struct host1x_syncpt *sp)
 	if (!sp)
 		return;
 
-	kref_put(&sp->ref, syncpt_release);
+	kref_put_mutex(&sp->ref, syncpt_release, &sp->host->syncpt_mutex);
 }
 EXPORT_SYMBOL(host1x_syncpt_put);