[Devel] [PATCH RHEL7 COMMIT] ub: properly charge and uncharge shmem

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-123.1.2-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-123.1.2.vz7.5.3
------>
commit 79d706d7d11a0d465930314657a8658ec20c4683
Author: Andrew Perepechko <panda at cloudlinux.com>
Date:   Tue May 19 18:05:29 2015 +0400

    ub: properly charge and uncharge shmem
    
    Currently, shmem_lock immediately and
    unconditionally uncharges what it has
    just charged for a lock request.
    
    This, indeed, causes a double uncharge
    with something like the following:
    
      shmid = shmget(12345, 8192, IPC_CREAT | 0666);
      rc = shmctl(shmid, SHM_LOCK, NULL);
      shmctl(shmid, IPC_RMID, 0);
    
    with the following in the kernel log:
    
    [  455.815025] Uncharging too much 2 h 0, res lockedpages ub 0
    
    Signed-off-by: Andrew Perepechko <panda at cloudlinux.com>
    Acked-by: Vladimir Davydov <vdavydov at parallels.com>
---
 mm/shmem.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index a6b3e30..d09a230 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1359,11 +1359,13 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
 		mapping_set_unevictable(file->f_mapping);
 	}
 	if (!lock && (info->flags & VM_LOCKED) && user) {
+		ub_lockedshm_uncharge(info, inode->i_size);
 		user_shm_unlock(inode->i_size, user);
 		info->flags &= ~VM_LOCKED;
 		mapping_clear_unevictable(file->f_mapping);
 	}
-	retval = 0;
+	spin_unlock(&info->lock);
+	return 0;
 
 out_nomem:
 	ub_lockedshm_uncharge(info, inode->i_size);