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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>
69 lines
1.6 KiB
C
69 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#include <linux/fs.h>
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#define DEVCG_ACC_MKNOD 1
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#define DEVCG_ACC_READ 2
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#define DEVCG_ACC_WRITE 4
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#define DEVCG_ACC_MASK (DEVCG_ACC_MKNOD | DEVCG_ACC_READ | DEVCG_ACC_WRITE)
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#define DEVCG_DEV_BLOCK 1
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#define DEVCG_DEV_CHAR 2
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#define DEVCG_DEV_ALL 4 /* this represents all devices */
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#if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
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int devcgroup_check_permission(short type, u32 major, u32 minor,
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short access);
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static inline int devcgroup_inode_permission(struct inode *inode, int mask)
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{
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short type, access = 0;
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if (likely(!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)))
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return 0;
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if (!inode->i_rdev)
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return 0;
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if (S_ISBLK(inode->i_mode))
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type = DEVCG_DEV_BLOCK;
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else /* S_ISCHR by the test above */
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type = DEVCG_DEV_CHAR;
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if (mask & MAY_WRITE)
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access |= DEVCG_ACC_WRITE;
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if (mask & MAY_READ)
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access |= DEVCG_ACC_READ;
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return devcgroup_check_permission(type, imajor(inode), iminor(inode),
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access);
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}
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static inline int devcgroup_inode_mknod(int mode, dev_t dev)
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{
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short type;
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if (!S_ISBLK(mode) && !S_ISCHR(mode))
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return 0;
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if (S_ISCHR(mode) && dev == WHITEOUT_DEV)
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return 0;
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if (S_ISBLK(mode))
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type = DEVCG_DEV_BLOCK;
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else
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type = DEVCG_DEV_CHAR;
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return devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
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DEVCG_ACC_MKNOD);
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}
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#else
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static inline int devcgroup_check_permission(short type, u32 major, u32 minor,
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short access)
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{ return 0; }
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static inline int devcgroup_inode_permission(struct inode *inode, int mask)
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{ return 0; }
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static inline int devcgroup_inode_mknod(int mode, dev_t dev)
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{ return 0; }
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#endif
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