From: Breno Leitao Date: Wed, 7 Jan 2026 14:06:36 +0000 (-0800) Subject: device_cgroup: remove branch hint after code refactor X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6784f274722559c0cdaaa418bc8b7b1d61c314f9;p=thirdparty%2Flinux.git device_cgroup: remove branch hint after code refactor commit 4ef4ac360101 ("device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()") reordered the checks in devcgroup_inode_permission() to check the inode mode before checking i_rdev, for better cache behavior. However, the likely() annotation on the i_rdev check was not updated to reflect the new code flow. Originally, when i_rdev was checked first, likely(!inode->i_rdev) made sense because most inodes were(?) regular files/directories, thus i_rdev == 0. After the reorder, by the time we reach the i_rdev check, we have already confirmed the inode IS a block or character device. Block and character special files are precisely defined by having a device number (i_rdev), so !inode->i_rdev is now the rare edge case, not the common case. Branch profiling confirmed this is 100% mispredicted: correct incorrect % Function File Line ------- --------- - -------- ---- ---- 0 2631904 100 devcgroup_inode_permission device_cgroup.h 24 Remove likely() to avoid giving the wrong hint to the CPU. Fixes: 4ef4ac360101 ("device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()") Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20260107-likely_device-v1-1-0c55f83a7e47@debian.org Reviewed-by: Mateusz Guzik Signed-off-by: Christian Brauner --- diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h index 0864773a57e8f..822085bc2d202 100644 --- a/include/linux/device_cgroup.h +++ b/include/linux/device_cgroup.h @@ -21,7 +21,7 @@ static inline int devcgroup_inode_permission(struct inode *inode, int mask) if (likely(!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))) return 0; - if (likely(!inode->i_rdev)) + if (!inode->i_rdev) return 0; if (S_ISBLK(inode->i_mode))