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Message-ID: <20191030111823.GE28525@quack2.suse.cz>
Date: Wed, 30 Oct 2019 12:18:23 +0100
From: Jan Kara <jack@...e.cz>
To: Matthew Bobrowski <mbobrowski@...browski.org>
Cc: tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v6 10/11] ext4: update ext4_sync_file() to not use
__generic_file_fsync()
On Mon 28-10-19 21:53:52, Matthew Bobrowski wrote:
> When the filesystem is created without a journal, we eventually call
> into __generic_file_fsync() in order to write out all the modified
> in-core data to the permanent storage device. This function happens to
> try and obtain an inode_lock() while synchronizing the files buffer
> and it's associated metadata.
>
> Generally, this is fine, however it becomes a problem when there is
> higher level code that has already obtained an inode_lock() as this
> leads to a recursive lock situation. This case is especially true when
> porting across direct I/O to iomap infrastructure as we obtain an
> inode_lock() early on in the I/O within ext4_dio_write_iter() and hold
> it until the I/O has been completed. Consequently, to not run into
> this specific issue, we move away from calling into
> __generic_file_fsync() and perform the necessary synchronization tasks
> within ext4_sync_file().
>
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
Nice! You can add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
>
> Thanks Jan and Christoph for the suggestion on this one, highly
> appreciated.
>
> fs/ext4/fsync.c | 72 ++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 47 insertions(+), 25 deletions(-)
>
> diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> index 5508baa11bb6..e10206e7f4bb 100644
> --- a/fs/ext4/fsync.c
> +++ b/fs/ext4/fsync.c
> @@ -80,6 +80,43 @@ static int ext4_sync_parent(struct inode *inode)
> return ret;
> }
>
> +static int ext4_fsync_nojournal(struct inode *inode, bool datasync,
> + bool *needs_barrier)
> +{
> + int ret, err;
> +
> + ret = sync_mapping_buffers(inode->i_mapping);
> + if (!(inode->i_state & I_DIRTY_ALL))
> + return ret;
> + if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> + return ret;
> +
> + err = sync_inode_metadata(inode, 1);
> + if (!ret)
> + ret = err;
> +
> + if (!ret)
> + ret = ext4_sync_parent(inode);
> + if (test_opt(inode->i_sb, BARRIER))
> + *needs_barrier = true;
> +
> + return ret;
> +}
> +
> +static int ext4_fsync_journal(struct inode *inode, bool datasync,
> + bool *needs_barrier)
> +{
> + struct ext4_inode_info *ei = EXT4_I(inode);
> + journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> + tid_t commit_tid = datasync ? ei->i_datasync_tid : ei->i_sync_tid;
> +
> + if (journal->j_flags & JBD2_BARRIER &&
> + !jbd2_trans_will_send_data_barrier(journal, commit_tid))
> + *needs_barrier = true;
> +
> + return jbd2_complete_transaction(journal, commit_tid);
> +}
> +
> /*
> * akpm: A new design for ext4_sync_file().
> *
> @@ -91,17 +128,14 @@ static int ext4_sync_parent(struct inode *inode)
> * What we do is just kick off a commit and wait on it. This will snapshot the
> * inode to disk.
> */
> -
> int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> {
> - struct inode *inode = file->f_mapping->host;
> - struct ext4_inode_info *ei = EXT4_I(inode);
> - journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> int ret = 0, err;
> - tid_t commit_tid;
> bool needs_barrier = false;
> + struct inode *inode = file->f_mapping->host;
> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>
> - if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
> + if (unlikely(ext4_forced_shutdown(sbi)))
> return -EIO;
>
> J_ASSERT(ext4_journal_current_handle() == NULL);
> @@ -111,23 +145,15 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> if (sb_rdonly(inode->i_sb)) {
> /* Make sure that we read updated s_mount_flags value */
> smp_rmb();
> - if (EXT4_SB(inode->i_sb)->s_mount_flags & EXT4_MF_FS_ABORTED)
> + if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)
> ret = -EROFS;
> goto out;
> }
>
> - if (!journal) {
> - ret = __generic_file_fsync(file, start, end, datasync);
> - if (!ret)
> - ret = ext4_sync_parent(inode);
> - if (test_opt(inode->i_sb, BARRIER))
> - goto issue_flush;
> - goto out;
> - }
> -
> ret = file_write_and_wait_range(file, start, end);
> if (ret)
> return ret;
> +
> /*
> * data=writeback,ordered:
> * The caller's filemap_fdatawrite()/wait will sync the data.
> @@ -142,18 +168,14 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> * (they were dirtied by commit). But that's OK - the blocks are
> * safe in-journal, which is all fsync() needs to ensure.
> */
> - if (ext4_should_journal_data(inode)) {
> + if (!sbi->s_journal)
> + ret = ext4_fsync_nojournal(inode, datasync, &needs_barrier);
> + else if (ext4_should_journal_data(inode))
> ret = ext4_force_commit(inode->i_sb);
> - goto out;
> - }
> + else
> + ret = ext4_fsync_journal(inode, datasync, &needs_barrier);
>
> - commit_tid = datasync ? ei->i_datasync_tid : ei->i_sync_tid;
> - if (journal->j_flags & JBD2_BARRIER &&
> - !jbd2_trans_will_send_data_barrier(journal, commit_tid))
> - needs_barrier = true;
> - ret = jbd2_complete_transaction(journal, commit_tid);
> if (needs_barrier) {
> - issue_flush:
> err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> if (!ret)
> ret = err;
> --
> 2.20.1
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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