commit 1f1cd7054fe7f45e65dd4963d0a38e5ab7a57cae
author Davidlohr Bueso <davidlohr@hp.com> Tue Jan 21 15:49:16 2014 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> Tue Jan 21 16:19:44 2014 -0800
tree 3296b8809eca9c4eb6db72a4d00d2c534b6c8db2
parent 363ee17f0f405faff74d9aaf93d21d5f41d5102d

mm/mlock: prepare params outside critical region

All mlock related syscalls prepare lock limits, lengths and start
parameters with the mmap_sem held.  Move this logic outside of the
critical region.  For the case of mlock, continue incrementing the
amount already locked by mm->locked_vm with the rwsem taken.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: Michel Lespinasse <walken@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mlock.c

diff --git a/mm/mlock.c b/mm/mlock.c
index 192e6ee..10819ed 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -709,19 +709,21 @@
 
 	lru_add_drain_all();	/* flush pagevec */
 
-	down_write(&current->mm->mmap_sem);
 	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 	start &= PAGE_MASK;
 
-	locked = len >> PAGE_SHIFT;
-	locked += current->mm->locked_vm;
-
 	lock_limit = rlimit(RLIMIT_MEMLOCK);
 	lock_limit >>= PAGE_SHIFT;
+	locked = len >> PAGE_SHIFT;
+
+	down_write(&current->mm->mmap_sem);
+
+	locked += current->mm->locked_vm;
 
 	/* check against resource limits */
 	if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 		error = do_mlock(start, len, 1);
+
 	up_write(&current->mm->mmap_sem);
 	if (!error)
 		error = __mm_populate(start, len, 0);
@@ -732,11 +734,13 @@
 {
 	int ret;
 
-	down_write(&current->mm->mmap_sem);
 	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 	start &= PAGE_MASK;
+
+	down_write(&current->mm->mmap_sem);
 	ret = do_mlock(start, len, 0);
 	up_write(&current->mm->mmap_sem);
+
 	return ret;
 }
 
@@ -781,12 +785,12 @@
 	if (flags & MCL_CURRENT)
 		lru_add_drain_all();	/* flush pagevec */
 
-	down_write(&current->mm->mmap_sem);
-
 	lock_limit = rlimit(RLIMIT_MEMLOCK);
 	lock_limit >>= PAGE_SHIFT;
 
 	ret = -ENOMEM;
+	down_write(&current->mm->mmap_sem);
+
 	if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 	    capable(CAP_IPC_LOCK))
 		ret = do_mlockall(flags);