[PATCH v1] mount: handle OOM on mnt_warn_timestamp_expiry

[Olaf Hering <olaf@aepfle.de>]

If no page could be allocated, an error pointer was used as format
string in pr_warn.

Rearrange the code to return early in case of OOM. Also add a check
for the return value of d_path. The API of that function is not
documented. It currently returns only ERR_PTR values, but may return
also NULL in the future. Use PTR_ERR_OR_ZERO to cover both cases.

Fixes: f8b92ba67c5d ("mount: Add mount warning for impending timestamp expiry")

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 fs/namespace.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 328087a4df8a..539d4f203a20 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2922,7 +2922,14 @@ static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *
 	   (!(sb->s_iflags & SB_I_TS_EXPIRY_WARNED)) &&
 	   (ktime_get_real_seconds() + TIME_UPTIME_SEC_MAX > sb->s_time_max)) {
 		char *buf = (char *)__get_free_page(GFP_KERNEL);
-		char *mntpath = buf ? d_path(mountpoint, buf, PAGE_SIZE) : ERR_PTR(-ENOMEM);
+		char *mntpath;
+		
+		if (!buf)
+			return;
+
+		mntpath = d_path(mountpoint, buf, PAGE_SIZE);
+		if (PTR_ERR_OR_ZERO(mntpath))
+			goto err;
 
 		pr_warn("%s filesystem being %s at %s supports timestamps until %ptTd (0x%llx)\n",
 			sb->s_type->name,
@@ -2930,8 +2937,9 @@ static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *
 			mntpath, &sb->s_time_max,
 			(unsigned long long)sb->s_time_max);
 
-		free_page((unsigned long)buf);
 		sb->s_iflags |= SB_I_TS_EXPIRY_WARNED;
+err:
+		free_page((unsigned long)buf);
 	}
 }