diff mbox series

[2/2] btrfs: Make btrfs_direct_write atomic with respect to inode_lock

Message ID f779c217a8599d71adec3b31e4afbac43df2a74c.1607449636.git.rgoldwyn@suse.com (mailing list archive)
State New, archived
Headers show
Series Fix direct write with respect to inode locking | expand

Commit Message

Goldwyn Rodrigues Dec. 8, 2020, 6:42 p.m. UTC 
From: Goldwyn Rodrigues <rgoldwyn@suse.com>

btrfs_direct_write() fallsback to buffered write in case btrfs is not
able to perform or complete a direct I/O. During the fallback
inode lock is unlocked and relocked. This does not guarantee the
atomicity of the entire write since the lock can be acquired by another
write between unlock and relock.

__btrfs_buffered_write() is used to perform the write without locks or
checks and called from btrfs_direct_write().

fa54fc76db94 ("btrfs: push inode locking and unlocking into buffered/direct write")
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/btrfs/file.c | 55 +++++++++++++++++++++++++++----------------------
 1 file changed, 30 insertions(+), 25 deletions(-)

Comments

Nikolay Borisov Dec. 10, 2020, 8:52 a.m. UTC | #1 
On 8.12.20 г. 20:42 ч., Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> btrfs_direct_write() fallsback to buffered write in case btrfs is not
> able to perform or complete a direct I/O. During the fallback
> inode lock is unlocked and relocked. This does not guarantee the
> atomicity of the entire write since the lock can be acquired by another
> write between unlock and relock.
> 
> __btrfs_buffered_write() is used to perform the write without locks or
> checks and called from btrfs_direct_write().
> 
> fa54fc76db94 ("btrfs: push inode locking and unlocking into buffered/direct write")
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>  fs/btrfs/file.c | 55 +++++++++++++++++++++++++++----------------------
>  1 file changed, 30 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 272660a8279f..03569fe20237 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1649,11 +1649,11 @@ static ssize_t btrfs_write_check(struct kiocb *iocb, struct iov_iter *from)
>  	return count;
>  }
>  
> -static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
> +static noinline ssize_t __btrfs_buffered_write(struct kiocb *iocb,
>  					       struct iov_iter *i)
>  {
>  	struct file *file = iocb->ki_filp;
> -	loff_t pos;
> +	loff_t pos = iocb->ki_pos;
>  	struct inode *inode = file_inode(file);
>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>  	struct page **pages = NULL;
> @@ -1667,20 +1667,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
>  	bool only_release_metadata = false;
>  	bool force_page_uptodate = false;
>  	loff_t old_isize = i_size_read(inode);
> -	unsigned int ilock_flags = 0;
> -
> -	if (iocb->ki_flags & IOCB_NOWAIT)
> -		ilock_flags |= BTRFS_ILOCK_TRY;
> -
> -	ret = btrfs_inode_lock(inode, ilock_flags);
> -	if (ret < 0)
> -		return ret;
> -
> -	ret = btrfs_write_check(iocb, i);
> -	if (ret <= 0)
> -		goto out;
>  
> -	pos = iocb->ki_pos;

Add lockdep_assert_held(&inode->i_rwsem); since __btrfs_buffered_write
does require the lock to be held.

<snip>
diff mbox series

Patch

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 272660a8279f..03569fe20237 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1649,11 +1649,11 @@  static ssize_t btrfs_write_check(struct kiocb *iocb, struct iov_iter *from)
 	return count;
 }
 
-static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
+static noinline ssize_t __btrfs_buffered_write(struct kiocb *iocb,
 					       struct iov_iter *i)
 {
 	struct file *file = iocb->ki_filp;
-	loff_t pos;
+	loff_t pos = iocb->ki_pos;
 	struct inode *inode = file_inode(file);
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	struct page **pages = NULL;
@@ -1667,20 +1667,7 @@  static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
 	bool only_release_metadata = false;
 	bool force_page_uptodate = false;
 	loff_t old_isize = i_size_read(inode);
-	unsigned int ilock_flags = 0;
-
-	if (iocb->ki_flags & IOCB_NOWAIT)
-		ilock_flags |= BTRFS_ILOCK_TRY;
-
-	ret = btrfs_inode_lock(inode, ilock_flags);
-	if (ret < 0)
-		return ret;
-
-	ret = btrfs_write_check(iocb, i);
-	if (ret <= 0)
-		goto out;
 
-	pos = iocb->ki_pos;
 	nrptrs = min(DIV_ROUND_UP(iov_iter_count(i), PAGE_SIZE),
 			PAGE_SIZE / (sizeof(struct page *)));
 	nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied);
@@ -1884,10 +1871,33 @@  static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
 		iocb->ki_pos += num_written;
 	}
 out:
-	btrfs_inode_unlock(inode, ilock_flags);
 	return num_written ? num_written : ret;
 }
 
+static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
+					       struct iov_iter *i)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	unsigned int ilock_flags = 0;
+	ssize_t ret;
+
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		ilock_flags |= BTRFS_ILOCK_TRY;
+
+	ret = btrfs_inode_lock(inode, ilock_flags);
+	if (ret < 0)
+		return ret;
+
+	ret = btrfs_write_check(iocb, i);
+	if (ret <= 0)
+		goto out;
+
+	ret = __btrfs_buffered_write(iocb, i);
+out:
+	btrfs_inode_unlock(inode, ilock_flags);
+	return ret;
+}
+
 static ssize_t check_direct_IO(struct btrfs_fs_info *fs_info,
 			       const struct iov_iter *iter, loff_t offset)
 {
@@ -1928,10 +1938,8 @@  static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
 		return err;
 
 	err = btrfs_write_check(iocb, from);
-	if (err <= 0) {
-		btrfs_inode_unlock(inode, ilock_flags);
+	if (err <= 0)
 		goto out;
-	}
 
 	pos = iocb->ki_pos;
 	/*
@@ -1945,16 +1953,12 @@  static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
 		goto relock;
 	}
 
-	if (check_direct_IO(fs_info, from, pos)) {
-		btrfs_inode_unlock(inode, ilock_flags);
+	if (check_direct_IO(fs_info, from, pos))
 		goto buffered;
-	}
 
 	dio = __iomap_dio_rw(iocb, from, &btrfs_dio_iomap_ops,
 			     &btrfs_dio_ops, is_sync_kiocb(iocb));
 
-	btrfs_inode_unlock(inode, ilock_flags);
-
 	if (IS_ERR_OR_NULL(dio)) {
 		err = PTR_ERR_OR_ZERO(dio);
 		if (err < 0 && err != -ENOTBLK)
@@ -1970,7 +1974,7 @@  static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
 
 buffered:
 	pos = iocb->ki_pos;
-	written_buffered = btrfs_buffered_write(iocb, from);
+	written_buffered = __btrfs_buffered_write(iocb, from);
 	if (written_buffered < 0) {
 		err = written_buffered;
 		goto out;
@@ -1991,6 +1995,7 @@  static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
 	invalidate_mapping_pages(file->f_mapping, pos >> PAGE_SHIFT,
 				 endbyte >> PAGE_SHIFT);
 out:
+	btrfs_inode_unlock(inode, ilock_flags);
 	return written ? written : err;
 }