diff options
| author | Breno Leitao <leitao@debian.org> | 2026-01-07 06:06:36 -0800 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2026-01-14 16:50:36 +0100 |
| commit | 6784f274722559c0cdaaa418bc8b7b1d61c314f9 (patch) | |
| tree | c5fa2999421dd6e5898a605c4fd11454c9c52d60 /include/linux | |
| parent | edecd1ae594abc8b14ed36c438d1a7db729403ba (diff) | |
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 <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>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/device_cgroup.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h index 0864773a57e8..822085bc2d20 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)) |