2017-07-05 03:33:28

by Goldwyn Rodrigues

Subject: [PATCH v2] btrfs: Correct assignment of pos

From: Goldwyn Rodrigues <[email protected]>

Assigning pos for usage early messes up in append mode, where
the pos is re-assigned in generic_write_checks(). Assign
pos later to get the correct position to write from iocb->ki_pos.

Since check_can_nocow also uses the value of pos, we shift
generic_write_checks() before check_can_nocow(). Checks with
IOCB_DIRECT are present in generic_write_checks(), so checking
for IOCB_NOWAIT is enough.

Also, put locking sequence in the fast path.

Changes since v1:
- Moved pos higher up to encompass check_can_nocow() call.

Fixes: edf064e7c6fe ("btrfs: nowait aio support")
Signed-off-by: Goldwyn Rodrigues <[email protected]>
---
fs/btrfs/file.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 59e2dccdf75b..ad53832838b5 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1875,16 +1875,25 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
ssize_t num_written = 0;
bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
ssize_t err;
- loff_t pos = iocb->ki_pos;
+ loff_t pos;
size_t count = iov_iter_count(from);
loff_t oldsize;
int clean_page = 0;

- if ((iocb->ki_flags & IOCB_NOWAIT) &&
- (iocb->ki_flags & IOCB_DIRECT)) {
- /* Don't sleep on inode rwsem */
- if (!inode_trylock(inode))
+ if (!inode_trylock(inode)) {
+ if (iocb->ki_flags & IOCB_NOWAIT)
return -EAGAIN;
+ inode_lock(inode);
+ }
+
+ err = generic_write_checks(iocb, from);
+ if (err <= 0) {
+ inode_unlock(inode);
+ return err;
+ }
+
+ pos = iocb->ki_pos;
+ if (iocb->ki_flags & IOCB_NOWAIT) {
/*
* We will allocate space in case nodatacow is not set,
* so bail
@@ -1895,13 +1904,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
inode_unlock(inode);
return -EAGAIN;
}
- } else
- inode_lock(inode);
-
- err = generic_write_checks(iocb, from);
- if (err <= 0) {
- inode_unlock(inode);
- return err;
}

current->backing_dev_info = inode_to_bdi(inode);
--
2.12.0

2017-07-07 16:17:59

by David Sterba

Subject: Re: [PATCH v2] btrfs: Correct assignment of pos

On Tue, Jul 04, 2017 at 10:33:07PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <[email protected]>
>
> Assigning pos for usage early messes up in append mode, where
> the pos is re-assigned in generic_write_checks(). Assign
> pos later to get the correct position to write from iocb->ki_pos.
>
> Since check_can_nocow also uses the value of pos, we shift
> generic_write_checks() before check_can_nocow(). Checks with
> IOCB_DIRECT are present in generic_write_checks(), so checking
> for IOCB_NOWAIT is enough.
>
> Also, put locking sequence in the fast path.
>
> Changes since v1:
> - Moved pos higher up to encompass check_can_nocow() call.
>
> Fixes: edf064e7c6fe ("btrfs: nowait aio support")
> Signed-off-by: Goldwyn Rodrigues <[email protected]>

Acked-by: David Sterba <[email protected]>

2017-07-10 23:04:01

by Liu Bo

Subject: Re: [PATCH v2] btrfs: Correct assignment of pos

On Tue, Jul 04, 2017 at 10:33:07PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <[email protected]>
>
> Assigning pos for usage early messes up in append mode, where
> the pos is re-assigned in generic_write_checks(). Assign
> pos later to get the correct position to write from iocb->ki_pos.
>
> Since check_can_nocow also uses the value of pos, we shift
> generic_write_checks() before check_can_nocow(). Checks with
> IOCB_DIRECT are present in generic_write_checks(), so checking
> for IOCB_NOWAIT is enough.
>
> Also, put locking sequence in the fast path.
>
> Changes since v1:
> - Moved pos higher up to encompass check_can_nocow() call.
>
> Fixes: edf064e7c6fe ("btrfs: nowait aio support")
> Signed-off-by: Goldwyn Rodrigues <[email protected]>
> ---
> fs/btrfs/file.c | 26 ++++++++++++++------------
> 1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 59e2dccdf75b..ad53832838b5 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1875,16 +1875,25 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> ssize_t num_written = 0;
> bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
> ssize_t err;
> - loff_t pos = iocb->ki_pos;
> + loff_t pos;
> size_t count = iov_iter_count(from);
> loff_t oldsize;
> int clean_page = 0;
>
> - if ((iocb->ki_flags & IOCB_NOWAIT) &&
> - (iocb->ki_flags & IOCB_DIRECT)) {
> - /* Don't sleep on inode rwsem */
> - if (!inode_trylock(inode))
> + if (!inode_trylock(inode)) {
> + if (iocb->ki_flags & IOCB_NOWAIT)
> return -EAGAIN;
> + inode_lock(inode);
> + }
> +
> + err = generic_write_checks(iocb, from);
> + if (err <= 0) {
> + inode_unlock(inode);
> + return err;
> + }
> +
> + pos = iocb->ki_pos;
> + if (iocb->ki_flags & IOCB_NOWAIT) {
> /*
> * We will allocate space in case nodatacow is not set,
> * so bail
> @@ -1895,13 +1904,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> inode_unlock(inode);
> return -EAGAIN;
> }
> - } else
> - inode_lock(inode);
> -
> - err = generic_write_checks(iocb, from);
> - if (err <= 0) {
> - inode_unlock(inode);
> - return err;
> }
>
> current->backing_dev_info = inode_to_bdi(inode);

Reviewed-by: Liu Bo <[email protected]>

-liubo