ufs: remove the BKL

This introduces a new per-superblock mutex in UFS to replace
the big kernel lock. I have been careful to avoid nested
calls to lock_ufs and to get the lock order right with
respect to other mutexes, in particular lock_super.

I did not make any attempt to prove that the big kernel
lock is not needed in a particular place in the code,
which is very possible.

The mutex has a significant performance impact, so it is only
used on SMP or PREEMPT configurations.

As Nick Piggin noticed, any allocation inside of the lock
may end up deadlocking when we get to ufs_getfrag_block
in the reclaim task, so we now use GFP_NOFS.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Nick Bowler <nbowler@elliptictech.com>
Cc: Evgeniy Dushistov <dushistov@mail.ru>
Cc: Nick Piggin <npiggin@gmail.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/fs/ufs/truncate.c b/fs/ufs/truncate.c
index a58f9155fc9..e56a4f56721 100644
--- a/fs/ufs/truncate.c
+++ b/fs/ufs/truncate.c
@@ -40,7 +40,6 @@
 #include <linux/time.h>
 #include <linux/stat.h>
 #include <linux/string.h>
-#include <linux/smp_lock.h>
 #include <linux/buffer_head.h>
 #include <linux/blkdev.h>
 #include <linux/sched.h>
@@ -467,7 +466,6 @@ int ufs_truncate(struct inode *inode, loff_t old_i_size)
 
         block_truncate_page(inode->i_mapping, inode->i_size, ufs_getfrag_block);
 
-        lock_kernel();
         while (1) {
                 retry = ufs_trunc_direct(inode);
                 retry |= ufs_trunc_indirect(inode, UFS_IND_BLOCK,
@@ -487,7 +485,6 @@ int ufs_truncate(struct inode *inode, loff_t old_i_size)
 
         inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
         ufsi->i_lastfrag = DIRECT_FRAGMENT;
-        unlock_kernel();
         mark_inode_dirty(inode);
 out:
         UFSD("EXIT: err %d\n", err);
@@ -510,7 +507,9 @@ int ufs_setattr(struct dentry *dentry, struct iattr *attr)
                 /* XXX(truncate): truncate_setsize should be called last */
                 truncate_setsize(inode, attr->ia_size);
 
+                lock_ufs(inode->i_sb);
                 error = ufs_truncate(inode, old_i_size);
+                unlock_ufs(inode->i_sb);
                 if (error)
                         return error;
         }