mm/shmem.c: fix unlikely() test of info->seals to test only for WRITE and GROW

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.

Link: http://lkml.kernel.org/r/20170203105656.7aec6237@gandalf.local.home
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: I83b8fc6ebae581486df16842713ba83a37e3b858

diff --git a/mm/shmem.c b/mm/shmem.c
index 28da0348982650d51632d19f2ce45e6160ad5c07..a7cf8c0371a2ba7ad560535a397084d7ec1f445d 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1528,7 +1528,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
        pgoff_t index = pos >> PAGE_CACHE_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)