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[PATCH 2/9] ext4: honor the O_SYNC flag for aysnchronous direct I/O requ

To: axboe@xxxxxxxxx, tytso@xxxxxxx, david@xxxxxxxxxxxxx, jmoyer@xxxxxxxxxx, bpm@xxxxxxx, viro@xxxxxxxxxxxxxxxxxx, jack@xxxxxxx
Subject: [PATCH 2/9] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests
From: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Date: Mon, 19 Nov 2012 23:41:31 -0800
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, hch@xxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20121120074116.24645.36369.stgit@xxxxxxxxxxxxxxxxxxx>
References: <20121120074116.24645.36369.stgit@xxxxxxxxxxxxxxxxxxx>
User-agent: StGit/0.15
If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get
flushed after the write completion.  Instead, it's flushed *before* the
I/O is sent to the disk (in __generic_file_aio_write).  This patch
attempts to fix that problem by marking an I/O as requiring a cache
flush in endio processing.  I'll send a follow-on patch to the
generic write code to get rid of the bogus generic_write_sync call
when EIOCBQUEUED is returned.

From: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
[darrick.wong@xxxxxxxxxx: Rework original patch to reflect a subsequent
                          ext4 reorganization]
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
 fs/ext4/ext4.h    |    9 +++++
 fs/ext4/file.c    |    2 +
 fs/ext4/inode.c   |    6 +++
 fs/ext4/page-io.c |   92 +++++++++++++++++++++++++++++++++++++++++++++--------
 fs/ext4/super.c   |   13 +++++++
 5 files changed, 106 insertions(+), 16 deletions(-)


diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3c20de1..f5a0b89 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -186,6 +186,7 @@ struct mpage_da_data {
 #define EXT4_IO_END_ERROR      0x0002
 #define EXT4_IO_END_QUEUED     0x0004
 #define EXT4_IO_END_DIRECT     0x0008
+#define EXT4_IO_END_NEEDS_SYNC 0x0010
 
 struct ext4_io_page {
        struct page     *p_page;
@@ -1279,6 +1280,9 @@ struct ext4_sb_info {
        /* workqueue for dio unwritten */
        struct workqueue_struct *dio_unwritten_wq;
 
+       /* workqueue for aio+dio+o_sync disk cache flushing */
+       struct workqueue_struct *aio_dio_flush_wq;
+
        /* timer for periodic error stats printing */
        struct timer_list s_err_report;
 
@@ -1335,6 +1339,11 @@ static inline void ext4_set_io_unwritten_flag(struct 
inode *inode,
        }
 }
 
+static inline int ext4_io_end_deferred(ext4_io_end_t *i)
+{
+       return i->flag & (EXT4_IO_END_UNWRITTEN | EXT4_IO_END_NEEDS_SYNC);
+}
+
 static inline ext4_io_end_t *ext4_inode_aio(struct inode *inode)
 {
        return inode->i_private;
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index bf3966b..dd34b81 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -155,7 +155,7 @@ ext4_file_dio_write(struct kiocb *iocb, const struct iovec 
*iov,
        ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
        mutex_unlock(&inode->i_mutex);
 
-       if (ret > 0 || ret == -EIOCBQUEUED) {
+       if (ret > 0) {
                ssize_t err;
 
                err = generic_write_sync(file, pos, ret);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b3c243b..fc4f05e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2893,8 +2893,12 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t 
offset,
 
        iocb->private = NULL;
 
+       /* AIO+DIO+O_SYNC I/Os need a cache flush after completion */
+       if (is_async && (IS_SYNC(inode) || (iocb->ki_filp->f_flags & O_DSYNC)))
+               io_end->flag |= EXT4_IO_END_NEEDS_SYNC;
+
        /* if not aio dio with unwritten extents, just free io and return */
-       if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
+       if (!ext4_io_end_deferred(io_end)) {
                ext4_free_io_end(io_end);
 out:
                if (is_async)
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 68e896e..cda013a 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -84,6 +84,50 @@ void ext4_free_io_end(ext4_io_end_t *io)
        kmem_cache_free(io_end_cachep, io);
 }
 
+/*
+ * This function is called in the completion path for AIO O_SYNC|O_DIRECT
+ * writes, and also in the fsync path.  The purpose is to ensure that the
+ * disk caches for the journal and data devices are flushed.
+ */
+static int ext4_end_io_do_flush(ext4_io_end_t *io)
+{
+       struct inode *inode = io->inode;
+       tid_t commit_tid;
+       bool needs_barrier = false;
+       journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
+       int barriers_enabled = test_opt(inode->i_sb, BARRIER);
+       int ret = 0;
+
+       if (!barriers_enabled)
+               return 0;
+
+       /*
+        * If we are running in nojournal mode, just flush the disk
+        * cache and return.
+        */
+       if (!journal)
+               return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL);
+
+       if (ext4_should_journal_data(inode)) {
+               ret = ext4_force_commit(inode->i_sb);
+               goto out;
+       }
+
+       commit_tid = io->iocb->ki_filp->f_flags & __O_SYNC ?
+               EXT4_I(inode)->i_sync_tid : EXT4_I(inode)->i_datasync_tid;
+       if (!jbd2_trans_will_send_data_barrier(journal, commit_tid))
+               needs_barrier = true;
+
+       jbd2_log_start_commit(journal, commit_tid);
+       ret = jbd2_log_wait_commit(journal, commit_tid);
+
+       if (!ret && needs_barrier)
+               ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL);
+
+out:
+       return ret;
+}
+
 /* check a range of space and convert unwritten extents to written. */
 static int ext4_end_io(ext4_io_end_t *io)
 {
@@ -96,21 +140,37 @@ static int ext4_end_io(ext4_io_end_t *io)
                   "list->prev 0x%p\n",
                   io, inode->i_ino, io->list.next, io->list.prev);
 
-       ret = ext4_convert_unwritten_extents(inode, offset, size);
-       if (ret < 0) {
-               ext4_msg(inode->i_sb, KERN_EMERG,
-                        "failed to convert unwritten extents to written "
-                        "extents -- potential data loss!  "
-                        "(inode %lu, offset %llu, size %zd, error %d)",
-                        inode->i_ino, offset, size, ret);
+       if (io->flag & EXT4_IO_END_UNWRITTEN) {
+               ret = ext4_convert_unwritten_extents(inode, offset, size);
+               if (ret < 0) {
+                       ext4_msg(inode->i_sb, KERN_EMERG,
+                                "failed to convert unwritten extents to "
+                                "written extents -- potential data loss!  "
+                                "(inode %lu, offset %llu, size %zd, error %d)",
+                                inode->i_ino, offset, size, ret);
+                       goto endio;
+               }
        }
+
+       /*
+        * This function has two callers.  The first is the end_io_work
+        * routine just below, which is an asynchronous completion context.
+        * The second is in the fsync path.  For the latter path, we can't
+        * return from here until the job is done.  Hence,
+        * ext4_end_io_do_flush is blocking.
+        */
+       if (io->flag & EXT4_IO_END_NEEDS_SYNC)
+               ret = ext4_end_io_do_flush(io);
+
+endio:
        if (io->iocb)
                aio_complete(io->iocb, io->result, 0);
 
        if (io->flag & EXT4_IO_END_DIRECT)
                inode_dio_done(inode);
        /* Wake up anyone waiting on unwritten extent conversion */
-       if (atomic_dec_and_test(&EXT4_I(inode)->i_unwritten))
+       if (io->flag & EXT4_IO_END_UNWRITTEN &&
+           atomic_dec_and_test(&EXT4_I(inode)->i_unwritten))
                wake_up_all(ext4_ioend_wq(io->inode));
        return ret;
 }
@@ -149,8 +209,11 @@ void ext4_add_complete_io(ext4_io_end_t *io_end)
        struct workqueue_struct *wq;
        unsigned long flags;
 
-       BUG_ON(!(io_end->flag & EXT4_IO_END_UNWRITTEN));
-       wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
+       BUG_ON(!ext4_io_end_deferred(io_end));
+       if (io_end->flag & EXT4_IO_END_UNWRITTEN)
+               wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
+       else
+               wq = EXT4_SB(io_end->inode->i_sb)->aio_dio_flush_wq;
 
        spin_lock_irqsave(&ei->i_completed_io_lock, flags);
        if (list_empty(&ei->i_completed_io_list)) {
@@ -180,7 +243,7 @@ static int ext4_do_flush_completed_IO(struct inode *inode,
 
        while (!list_empty(&unwritten)) {
                io = list_entry(unwritten.next, ext4_io_end_t, list);
-               BUG_ON(!(io->flag & EXT4_IO_END_UNWRITTEN));
+               BUG_ON(!ext4_io_end_deferred(io));
                list_del_init(&io->list);
 
                err = ext4_end_io(io);
@@ -192,7 +255,8 @@ static int ext4_do_flush_completed_IO(struct inode *inode,
        spin_lock_irqsave(&ei->i_completed_io_lock, flags);
        while (!list_empty(&complete)) {
                io = list_entry(complete.next, ext4_io_end_t, list);
-               io->flag &= ~EXT4_IO_END_UNWRITTEN;
+               io->flag &= ~(EXT4_IO_END_UNWRITTEN |
+                             EXT4_IO_END_NEEDS_SYNC);
                /* end_io context can not be destroyed now because it still
                 * used by queued worker. Worker thread will destroy it later */
                if (io->flag & EXT4_IO_END_QUEUED)
@@ -204,7 +268,7 @@ static int ext4_do_flush_completed_IO(struct inode *inode,
         * flag, and destroy it's end_io if it was converted already */
        if (work_io) {
                work_io->flag &= ~EXT4_IO_END_QUEUED;
-               if (!(work_io->flag & EXT4_IO_END_UNWRITTEN))
+               if (!ext4_io_end_deferred(work_io))
                        list_add_tail(&work_io->list, &to_free);
        }
        spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
@@ -319,7 +383,7 @@ static void ext4_end_bio(struct bio *bio, int error)
                             bi_sector >> (inode->i_blkbits - 9));
        }
 
-       if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
+       if (!ext4_io_end_deferred(io_end)) {
                ext4_free_io_end(io_end);
                return;
        }
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 80928f7..c657c4d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -849,7 +849,9 @@ static void ext4_put_super(struct super_block *sb)
        dquot_disable(sb, -1, DQUOT_USAGE_ENABLED | DQUOT_LIMITS_ENABLED);
 
        flush_workqueue(sbi->dio_unwritten_wq);
+       flush_workqueue(sbi->aio_dio_flush_wq);
        destroy_workqueue(sbi->dio_unwritten_wq);
+       destroy_workqueue(sbi->aio_dio_flush_wq);
 
        if (sbi->s_journal) {
                err = jbd2_journal_destroy(sbi->s_journal);
@@ -3913,6 +3915,14 @@ no_journal:
                goto failed_mount_wq;
        }
 
+       EXT4_SB(sb)->aio_dio_flush_wq =
+               alloc_workqueue("ext4-aio-dio-flush",
+                               WQ_MEM_RECLAIM | WQ_UNBOUND, 1);
+       if (!EXT4_SB(sb)->aio_dio_flush_wq) {
+               pr_err("EXT4-fs: failed to create flush workqueue\n");
+               goto failed_flush_wq;
+       }
+
        /*
         * The jbd2_journal_load will have done any necessary log recovery,
         * so we can safely mount the rest of the filesystem now.
@@ -4045,6 +4055,8 @@ failed_mount4a:
        sb->s_root = NULL;
 failed_mount4:
        ext4_msg(sb, KERN_ERR, "mount failed");
+       destroy_workqueue(EXT4_SB(sb)->aio_dio_flush_wq);
+failed_flush_wq:
        destroy_workqueue(EXT4_SB(sb)->dio_unwritten_wq);
 failed_mount_wq:
        if (sbi->s_journal) {
@@ -4494,6 +4506,7 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
 
        trace_ext4_sync_fs(sb, wait);
        flush_workqueue(sbi->dio_unwritten_wq);
+       flush_workqueue(sbi->aio_dio_flush_wq);
        /*
         * Writeback quota in non-journalled quota case - journalled quota has
         * no dirty dquots

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