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>

1 files changed, 11 insertions, 7 deletions

diff --git a/mm/mlock.c b/mm/mlock.c
index 192e6eebe4f2..10819ed4df3e 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -709,19 +709,21 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 
         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 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 {
         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 @@ SYSCALL_DEFINE1(mlockall, int, flags)
         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);