diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2023-11-26 12:24:38 -0800 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2023-12-12 14:24:13 +0100 |
| commit | 253ca8678d30bcf94410b54476fc1e0f1627a137 (patch) | |
| tree | 4727be75e2660bf1a1a54701f16dddb74a35b335 /include | |
| parent | 7cb537b6f6d7d6529be04139178f929d9a63b918 (diff) | |
Improve __fget_files_rcu() code generation (and thus __fget_light())
Commit 0ede61d8589c ("file: convert to SLAB_TYPESAFE_BY_RCU") caused a
performance regression as reported by the kernel test robot.
The __fget_light() function is one of those critical ones for some
loads, and the code generation was unnecessarily impacted. Let's just
write that function to better.
Reported-by: kernel test robot <oliver.sang@intel.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Closes: https://lore.kernel.org/oe-lkp/202311201406.2022ca3f-oliver.sang@intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/CAHk-=wiCJtLbFWNURB34b9a_R_unaH3CiMRXfkR0-iihB_z68A@mail.gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/fdtable.h | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index bc4c3287a65e..80bd7789bab1 100644 --- a/include/linux/fdtable.h +++ b/include/linux/fdtable.h @@ -83,12 +83,17 @@ struct dentry; static inline struct file *files_lookup_fd_raw(struct files_struct *files, unsigned int fd) { struct fdtable *fdt = rcu_dereference_raw(files->fdt); - - if (fd < fdt->max_fds) { - fd = array_index_nospec(fd, fdt->max_fds); - return rcu_dereference_raw(fdt->fd[fd]); - } - return NULL; + unsigned long mask = array_index_mask_nospec(fd, fdt->max_fds); + struct file *needs_masking; + + /* + * 'mask' is zero for an out-of-bounds fd, all ones for ok. + * 'fd&mask' is 'fd' for ok, or 0 for out of bounds. + * + * Accessing fdt->fd[0] is ok, but needs masking of the result. + */ + needs_masking = rcu_dereference_raw(fdt->fd[fd&mask]); + return (struct file *)(mask & (unsigned long)needs_masking); } static inline struct file *files_lookup_fd_locked(struct files_struct *files, unsigned int fd) |