Merge patch series "two nits for path lookup"

Mateusz Guzik <mjguzik@gmail.com> says:

Since path looku is being looked at, two extra nits from me:

1. some trivial jump avoidance in inode_permission()

2. but more importantly avoiding a memory access which is most likely a
cache miss when descending into devcgroup_inode_permission()

the file seems to have no maintainer fwiw

anyhow I'm confident the way forward is to add IOP_FAST_MAY_EXEC (or
similar) to elide inode_permission() in the common case to begin with.
There are quite a few branches which straight up don't need execute.
On top of that btrfs has a permission hook only to check for MAY_WRITE,
which in case of path lookup is not set. With the above flag the call
will be avoided.

* patches from https://lore.kernel.org/20250416221626.2710239-1-mjguzik@gmail.com:
  device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()
  fs: touch up predicts in inode_permission()

Link: https://lore.kernel.org/20250416221626.2710239-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 9 insertions, 8 deletions

diff --git a/fs/namei.c b/fs/namei.c
index b9cc03faa033..b051211f064c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -571,14 +571,14 @@ int inode_permission(struct mnt_idmap *idmap,
 	int retval;
 
 	retval = sb_permission(inode->i_sb, inode, mask);
-	if (retval)
+	if (unlikely(retval))
 		return retval;
 
 	if (unlikely(mask & MAY_WRITE)) {
 		/*
 		 * Nobody gets write access to an immutable file.
 		 */
-		if (IS_IMMUTABLE(inode))
+		if (unlikely(IS_IMMUTABLE(inode)))
 			return -EPERM;
 
 		/*
@@ -586,16 +586,16 @@ int inode_permission(struct mnt_idmap *idmap,
 		 * written back improperly if their true value is unknown
 		 * to the vfs.
 		 */
-		if (HAS_UNMAPPED_ID(idmap, inode))
+		if (unlikely(HAS_UNMAPPED_ID(idmap, inode)))
 			return -EACCES;
 	}
 
 	retval = do_inode_permission(idmap, inode, mask);
-	if (retval)
+	if (unlikely(retval))
 		return retval;
 
 	retval = devcgroup_inode_permission(inode, mask);
-	if (retval)
+	if (unlikely(retval))
 		return retval;
 
 	return security_inode_permission(inode, mask);
diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
index d02f32b7514e..0864773a57e8 100644
--- a/include/linux/device_cgroup.h
+++ b/include/linux/device_cgroup.h
@@ -18,15 +18,16 @@ static inline int devcgroup_inode_permission(struct inode *inode, int mask)
 {
 	short type, access = 0;
 
+	if (likely(!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)))
+		return 0;
+
 	if (likely(!inode->i_rdev))
 		return 0;
 
 	if (S_ISBLK(inode->i_mode))
 		type = DEVCG_DEV_BLOCK;
-	else if (S_ISCHR(inode->i_mode))
+	else /* S_ISCHR by the test above */
 		type = DEVCG_DEV_CHAR;
-	else
-		return 0;
 
 	if (mask & MAY_WRITE)
 		access |= DEVCG_ACC_WRITE;