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authorJeff Layton <jeff.layton@primarydata.com>2015-04-03 16:04:04 +0300
committerJeff Layton <jeff.layton@primarydata.com>2015-04-03 16:04:04 +0300
commit0429c2b5c1c4c8ba6cd563c1964baf3ed238df26 (patch)
tree60bda1e72adfea7a0a4fe3cdceacc78a3f0e8844
parent3648888e90bb7fe6d0586ec177511e6678ee22c3 (diff)
downloadlinux-0429c2b5c1c4c8ba6cd563c1964baf3ed238df26.tar.xz
locks: use cmpxchg to assign i_flctx pointer
During the v3.20/v4.0 cycle, I had originally had the code manage the inode->i_flctx pointer using a compare-and-swap operation instead of the i_lock. Sasha Levin though hit a problem while testing with trinity that made me believe that that wasn't safe. At the time, changing the code to protect the i_flctx pointer seemed to fix the issue, but I now think that was just coincidence. The issue was likely the same race that Kirill Shutemov hit while testing the pre-rc1 v4.0 kernel and that Linus spotted. Due to the way that the spinlock was dropped in the middle of flock_lock_file, you could end up with multiple flock locks for the same struct file on the inode. Reinstate the use of a CAS operation to assign this pointer since it's likely to be more efficient and gets the i_lock completely out of the file locking business. Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
-rw-r--r--fs/locks.c9
1 files changed, 1 insertions, 8 deletions
diff --git a/fs/locks.c b/fs/locks.c
index 16cae1a00851..52b780fb5258 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -223,14 +223,7 @@ locks_get_lock_context(struct inode *inode, int type)
* Assign the pointer if it's not already assigned. If it is, then
* free the context we just allocated.
*/
- spin_lock(&inode->i_lock);
- if (likely(!inode->i_flctx)) {
- inode->i_flctx = new;
- new = NULL;
- }
- spin_unlock(&inode->i_lock);
-
- if (new)
+ if (cmpxchg(&inode->i_flctx, NULL, new))
kmem_cache_free(flctx_cache, new);
out:
return inode->i_flctx;