[PATCH 1/9] vfs: Handle O_SYNC AIO DIO in generic code properly

Darrick J. Wong
2012-11-20T07:41:55Z

Provide VFS helpers for handling O_SYNC AIO DIO writes. Filesystems wanting to
use the helpers have to pass DIO_SYNC_WRITES to __blockdev_direct_IO. If the
filesystem doesn't provide its own direct IO end_io handler, the generic code
will take care of issuing the flush. Otherwise, the filesystem's custom end_io
handler is passed struct dio_sync_io_work pointer as 'private' argument, and it
must call generic_dio_end_io() to finish the AIO DIO. The generic code then
takes care to call generic_write_sync() from a workqueue context when AIO DIO
is complete.

Since all filesystems using blockdev_direct_IO() need O_SYNC aio dio handling
and the generic suffices for them, make blockdev_direct_IO() pass the new
DIO_SYNC_WRITES flag.

From: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
[darrick.wong@oracle.com: Minor style and changelog fixes]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/direct-io.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++--
fs/super.c | 2 +
include/linux/fs.h | 14 +++++-
3 files changed, 137 insertions(+), 5 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index f86c720..b7391d4 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -37,6 +37,7 @@
#include <linux/uio.h>
#include <linux/atomic.h>
#include <linux/prefetch.h>
+#include <asm/cmpxchg.h>

/*
* How many user pages to map in one call to get_user_pages(). This determines
@@ -112,6 +113,15 @@ struct dio_submit {
unsigned tail; /* last valid page + 1 */
};

+/* state needed for final sync and completion of O_SYNC AIO DIO */
+struct dio_sync_io_work {
+ struct kiocb *iocb;
+ loff_t offset;
+ ssize_t len;
+ int ret;
+ struct work_struct work;
+};
+
/* dio_state communicated between submission path and end_io */
struct dio {
int flags; /* doesn't change */
@@ -134,6 +144,7 @@ struct dio {
/* AIO related stuff */
struct kiocb *iocb; /* kiocb */
ssize_t result; /* IO result */
+ struct dio_sync_io_work *sync_work; /* work used for O_SYNC AIO */

/*
* pages[] (and any fields placed after it) are not zeroed out at
@@ -217,6 +228,45 @@ static inline struct page *dio_get_page(struct dio *dio,
}

/**
+ * generic_dio_end_io() - generic dio ->end_io handler
+ * @iocb: iocb of finishing DIO
+ * @offset: the byte offset in the file of the completed operation
+ * @bytes: length of the completed operation
+ * @work: work to queue for O_SYNC AIO DIO, NULL otherwise
+ * @ret: error code if IO failed
+ * @is_async: is this AIO?
+ *
+ * This is generic callback to be called when direct IO is finished. It
+ * handles update of number of outstanding DIOs for an inode, completion
+ * of async iocb and queueing of work if we need to call fsync() because
+ * io was O_SYNC.
+ */
+void generic_dio_end_io(struct kiocb *iocb, loff_t offset, ssize_t bytes,
+ struct dio_sync_io_work *work, int ret, bool is_async)
+{
+ struct inode *inode = iocb->ki_filp->f_dentry->d_inode;
+
+ if (!is_async) {
+ inode_dio_done(inode);
+ return;
+ }
+
+ /*
+ * If we need to sync file, we offload completion to workqueue
+ */
+ if (work) {
+ work->ret = ret;
+ work->offset = offset;
+ work->len = bytes;
+ queue_work(inode->i_sb->s_dio_flush_wq, &work->work);
+ } else {
+ aio_complete(iocb, ret, 0);
+ inode_dio_done(inode);
+ }
+}
+EXPORT_SYMBOL(generic_dio_end_io);
+
+/**
* dio_complete() - called when all DIO BIO I/O has been completed
* @offset: the byte offset in the file of the completed operation
*
@@ -258,12 +308,23 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is
ret = transferred;

if (dio->end_io && dio->result) {
+ void *private;
+
+ if (dio->sync_work)
+ private = dio->sync_work;
+ else
+ private = dio->private;
+
dio->end_io(dio->iocb, offset, transferred,
- dio->private, ret, is_async);
+ private, ret, is_async);
} else {
- if (is_async)
- aio_complete(dio->iocb, ret, 0);
- inode_dio_done(dio->inode);
+ /* No IO submitted? Skip syncing... */
+ if (!dio->result && dio->sync_work) {
+ kfree(dio->sync_work);
+ dio->sync_work = NULL;
+ }
+ generic_dio_end_io(dio->iocb, offset, transferred,
+ dio->sync_work, ret, is_async);
}

return ret;
@@ -1020,6 +1081,41 @@ static inline int drop_refcount(struct dio *dio)
}

/*
+ * Work performed from workqueue when AIO DIO is finished.
+ */
+static void dio_aio_sync_work(struct work_struct *work)
+{
+ struct dio_sync_io_work *sync_work =
+ container_of(work, struct dio_sync_io_work, work);
+ struct kiocb *iocb = sync_work->iocb;
+ struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
+ int err, ret = sync_work->ret;
+
+ err = generic_write_sync(iocb->ki_filp, sync_work->offset,
+ sync_work->len);
+ if (err < 0 && ret > 0)
+ ret = err;
+ aio_complete(iocb, ret, 0);
+ inode_dio_done(inode);
+}
+
+static noinline int dio_create_flush_wq(struct super_block *sb)
+{
+ struct workqueue_struct *wq =
+ alloc_workqueue("dio-sync", WQ_UNBOUND, 1);
+
+ if (!wq)
+ return -ENOMEM;
+ /*
+ * Atomically put workqueue in place. Release our one in case someone
+ * else won the race and attached workqueue to superblock.
+ */
+ if (cmpxchg(&sb->s_dio_flush_wq, NULL, wq))
+ destroy_workqueue(wq);
+ return 0;
+}
+
+/*
* This is a library function for use by filesystem drivers.
*
* The locking rules are governed by the flags parameter:
@@ -1112,6 +1208,26 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
memset(dio, 0, offsetof(struct dio, pages));

dio->flags = flags;
+ if (flags & DIO_SYNC_WRITES && rw & WRITE &&
+ ((iocb->ki_filp->f_flags & O_DSYNC) || IS_SYNC(inode))) {
+ /* The first O_SYNC AIO DIO for this FS? Create workqueue... */
+ if (!inode->i_sb->s_dio_flush_wq) {
+ retval = dio_create_flush_wq(inode->i_sb);
+ if (retval) {
+ kmem_cache_free(dio_cache, dio);
+ goto out;
+ }
+ }
+ dio->sync_work = kmalloc(sizeof(struct dio_sync_io_work),
+ GFP_KERNEL);
+ if (!dio->sync_work) {
+ retval = -ENOMEM;
+ kmem_cache_free(dio_cache, dio);
+ goto out;
+ }
+ INIT_WORK(&dio->sync_work->work, dio_aio_sync_work);
+ dio->sync_work->iocb = iocb;
+ }
if (dio->flags & DIO_LOCKING) {
if (rw == READ) {
struct address_space *mapping =
@@ -1124,6 +1240,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
end - 1);
if (retval) {
mutex_unlock(&inode->i_mutex);
+ kfree(dio->sync_work);
kmem_cache_free(dio_cache, dio);
goto out;
}
@@ -1271,6 +1388,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,

if (drop_refcount(dio) == 0) {
retval = dio_complete(dio, offset, retval, false);
+ kfree(dio->sync_work);
kmem_cache_free(dio_cache, dio);
} else
BUG_ON(retval != -EIOCBQUEUED);
diff --git a/fs/super.c b/fs/super.c
index 12f1237..7478202 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -244,6 +244,8 @@ static inline void destroy_super(struct super_block *s)
#ifdef CONFIG_SMP
free_percpu(s->s_files);
#endif
+ if (s->s_dio_flush_wq)
+ destroy_workqueue(s->s_dio_flush_wq);
destroy_sb_writers(s);
security_sb_free(s);
WARN_ON(!list_empty(&s->s_mounts));
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b33cfc9..40dd206 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -44,6 +44,7 @@ struct vm_area_struct;
struct vfsmount;
struct cred;
struct swap_info_struct;
+struct workqueue_struct;

extern void __init inode_init(void);
extern void __init inode_init_early(void);
@@ -1321,6 +1322,9 @@ struct super_block {

/* Being remounted read-only */
int s_readonly_remount;
+
+ /* Pending fsync calls for completed AIO DIO with O_SYNC */
+ struct workqueue_struct *s_dio_flush_wq;
};

/* superblock cache pruning functions */
@@ -2433,8 +2437,13 @@ enum {

/* filesystem does not support filling holes */
DIO_SKIP_HOLES = 0x02,
+
+ /* need generic handling of O_SYNC aio writes */
+ DIO_SYNC_WRITES = 0x04,
};

+struct dio_sync_io_work;
+
void dio_end_io(struct bio *bio, int error);

ssize_t __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
@@ -2448,12 +2457,15 @@ static inline ssize_t blockdev_direct_IO(int rw, struct kiocb *iocb,
{
return __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
offset, nr_segs, get_block, NULL, NULL,
- DIO_LOCKING | DIO_SKIP_HOLES);
+ DIO_LOCKING | DIO_SKIP_HOLES |
+ DIO_SYNC_WRITES);
}
#endif

void inode_dio_wait(struct inode *inode);
void inode_dio_done(struct inode *inode);
+void generic_dio_end_io(struct kiocb *iocb, loff_t offset, ssize_t bytes,
+ struct dio_sync_io_work *work, int ret, bool is_async);

extern const struct file_operations generic_ro_fops;