mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-03-22 07:27:12 +08:00
6784f27472
commit4ef4ac3601("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:4ef4ac3601("device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()") Signed-off-by: Breno Leitao <leitao@debian.org> Link: https://patch.msgid.link/20260107-likely_device-v1-1-0c55f83a7e47@debian.org Reviewed-by: Mateusz Guzik <mjguzik@gmail.com> Signed-off-by: Christian Brauner <brauner@kernel.org>