Commit 3f472cc9 authored Feb 24, 2017 by Steven Rostedt (VMware) Committed by Linus Torvalds Feb 24, 2017

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>

parent c2f83143

mm/shmem.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -2331,7 +2331,7 @@ 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)