direct-io: Implement generic deferred AIO completions

Add support to the core direct-io code to defer AIO completions to user
context using a workqueue.  This replaces opencoded and less efficient
code in XFS and ext4 (we save a memory allocation for each direct IO)
and will be needed to properly support O_(D)SYNC for AIO.

The communication between the filesystem and the direct I/O code requires
a new buffer head flag, which is a bit ugly but not avoidable until the
direct I/O code stops abusing the buffer_head structure for communicating
with the filesystems.

Currently this creates a per-superblock unbound workqueue for these
completions, which is taken from an earlier patch by Jan Kara.  I'm
not really convinced about this use and would prefer a "normal" global
workqueue with a high concurrency limit, but this needs further discussion.

JK: Fixed ext4 part, dynamic allocation of the workqueue.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 9 insertions, 9 deletions

diff --git a/fs/super.c b/fs/super.c
index 68307c029228..5536a95186e2 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -152,15 +152,9 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
         static const struct super_operations default_op;
 
         if (s) {
-                if (security_sb_alloc(s)) {
-                        /*
-                         * We cannot call security_sb_free() without
-                         * security_sb_alloc() succeeding. So bail out manually
-                         */
-                        kfree(s);
-                        s = NULL;
-                        goto out;
-                }
+                if (security_sb_alloc(s))
+                        goto out_free_sb;
+
 #ifdef CONFIG_SMP
                 s->s_files = alloc_percpu(struct list_head);
                 if (!s->s_files)
@@ -228,6 +222,7 @@ err_out:
                 free_percpu(s->s_files);
 #endif
         destroy_sb_writers(s);
+out_free_sb:
         kfree(s);
         s = NULL;
         goto out;
@@ -414,6 +409,11 @@ void generic_shutdown_super(struct super_block *sb)
 
                 evict_inodes(sb);
 
+                if (sb->s_dio_done_wq) {
+                        destroy_workqueue(sb->s_dio_done_wq);
+                        sb->s_dio_done_wq = NULL;
+                }
+
                 if (sop->put_super)
                         sop->put_super(sb);