On Fri, 3 Feb 2017, Steven Rostedt (VMware) wrote:
> From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
>
> Running my likely/unlikely profiler, I discovered that the test in
> shmem_write_begin() that tests for info->seals as unlikely, is
> always incorrect. This is because shmem_get_inode() sets info->seals to
> have F_SEAL_SEAL set by default, and it is unlikely to be cleared when
> shmem_write_begin() is called. Thus, the if statement is very likely.
>
> But as the if statement block only cares about F_SEAL_WRITE and
> F_SEAL_GROW, change the test to only test those two bits.
>
> Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
Acked-by: Hugh Dickins <hu...@google.com>
> ---
> mm/shmem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index bb53285..ef4cdbb 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2194,7 +2194,7 @@ shmem_write_begin(struct file *file, struct
> address_space *mapping,
> pgoff_t index = pos >> PAGE_SHIFT;
>
> /* i_mutex is held by caller */
> - if (unlikely(info->seals)) {
> + if (unlikely(info->seals & (F_SEAL_WRITE | F_SEAL_GROW))) {
> if (info->seals & F_SEAL_WRITE)
> return -EPERM;
> if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
> --
> 2.9.3
