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 trinity that made me believe that that wasn't safe. I now think though that I completely misread the problem, even though it seemed like it went away when we started using the i_lock to protect this pointer. 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 <[email protected]> --- fs/locks.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index 4347f3dc17cc..22c0785c00ed 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; -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
