From: Zhang Yi <[email protected]>
Increase i_size in iomap_zero_range() and iomap_unshare_iter() is not
needed, the caller should handle it. Especially, when truncate partial
block, we could not increase i_size beyond the new EOF here. It doesn't
affect xfs and gfs2 now because they set the new file size after zero
out, it doesn't matter that a transient increase in i_size, but it will
affect ext4 because it set file size before truncate. At the same time,
iomap_write_failed() is also not needed for above two cases too, so
factor them out and move them to iomap_write_iter() and
iomap_zero_iter().
Signed-off-by: Zhang Yi <[email protected]>
---
fs/iomap/buffered-io.c | 59 +++++++++++++++++++++---------------------
1 file changed, 30 insertions(+), 29 deletions(-)
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 093c4515b22a..19f91324c690 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -786,7 +786,6 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
out_unlock:
__iomap_put_folio(iter, pos, 0, folio);
- iomap_write_failed(iter->inode, pos, len);
return status;
}
@@ -838,34 +837,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
size_t copied, struct folio *folio)
{
const struct iomap *srcmap = iomap_iter_srcmap(iter);
- loff_t old_size = iter->inode->i_size;
- size_t ret;
-
- if (srcmap->type == IOMAP_INLINE) {
- ret = iomap_write_end_inline(iter, folio, pos, copied);
- } else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
- ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
- copied, &folio->page, NULL);
- } else {
- ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
- }
- /*
- * Update the in-memory inode size after copying the data into the page
- * cache. It's up to the file system to write the updated size to disk,
- * preferably after I/O completion so that no stale data is exposed.
- */
- if (pos + ret > old_size) {
- i_size_write(iter->inode, pos + ret);
- iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
- }
- __iomap_put_folio(iter, pos, ret, folio);
-
- if (old_size < pos)
- pagecache_isize_extended(iter->inode, old_size, pos);
- if (ret < len)
- iomap_write_failed(iter->inode, pos + ret, len - ret);
- return ret;
+ if (srcmap->type == IOMAP_INLINE)
+ return iomap_write_end_inline(iter, folio, pos, copied);
+ if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
+ return block_write_end(NULL, iter->inode->i_mapping, pos, len,
+ copied, &folio->page, NULL);
+ return __iomap_write_end(iter->inode, pos, len, copied, folio);
}
static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
@@ -880,6 +858,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
do {
struct folio *folio;
+ loff_t old_size;
size_t offset; /* Offset into folio */
size_t bytes; /* Bytes to write to folio */
size_t copied; /* Bytes copied from user */
@@ -912,8 +891,10 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
}
status = iomap_write_begin(iter, pos, bytes, &folio);
- if (unlikely(status))
+ if (unlikely(status)) {
+ iomap_write_failed(iter->inode, pos, bytes);
break;
+ }
if (iter->iomap.flags & IOMAP_F_STALE)
break;
@@ -927,6 +908,24 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
status = iomap_write_end(iter, pos, bytes, copied, folio);
+ /*
+ * Update the in-memory inode size after copying the data into
+ * the page cache. It's up to the file system to write the
+ * updated size to disk, preferably after I/O completion so that
+ * no stale data is exposed.
+ */
+ old_size = iter->inode->i_size;
+ if (pos + status > old_size) {
+ i_size_write(iter->inode, pos + status);
+ iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
+ }
+ __iomap_put_folio(iter, pos, status, folio);
+
+ if (old_size < pos)
+ pagecache_isize_extended(iter->inode, old_size, pos);
+ if (status < bytes)
+ iomap_write_failed(iter->inode, pos + status,
+ bytes - status);
if (unlikely(copied != status))
iov_iter_revert(i, copied - status);
@@ -1296,6 +1295,7 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
bytes = folio_size(folio) - offset;
bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
+ __iomap_put_folio(iter, pos, bytes, folio);
if (WARN_ON_ONCE(bytes == 0))
return -EIO;
@@ -1360,6 +1360,7 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
folio_mark_accessed(folio);
bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
+ __iomap_put_folio(iter, pos, bytes, folio);
if (WARN_ON_ONCE(bytes == 0))
return -EIO;
--
2.39.2
On Mon, Mar 11, 2024 at 08:22:54PM +0800, Zhang Yi wrote:
> From: Zhang Yi <[email protected]>
>
> Increase i_size in iomap_zero_range() and iomap_unshare_iter() is not
> needed, the caller should handle it. Especially, when truncate partial
> block, we could not increase i_size beyond the new EOF here. It doesn't
> affect xfs and gfs2 now because they set the new file size after zero
> out, it doesn't matter that a transient increase in i_size, but it will
> affect ext4 because it set file size before truncate.
> At the same time,
> iomap_write_failed() is also not needed for above two cases too, so
> factor them out and move them to iomap_write_iter() and
> iomap_zero_iter().
This change should be a separate patch with its own justification.
Which is, AFAICT, something along the lines of:
"Unsharing and zeroing can only happen within EOF, so there is never a
need to perform posteof pagecache truncation if write begin fails."
> Signed-off-by: Zhang Yi <[email protected]>
Doesn't this patch fix a bug in ext4?
> ---
> fs/iomap/buffered-io.c | 59 +++++++++++++++++++++---------------------
> 1 file changed, 30 insertions(+), 29 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 093c4515b22a..19f91324c690 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -786,7 +786,6 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
>
> out_unlock:
> __iomap_put_folio(iter, pos, 0, folio);
> - iomap_write_failed(iter->inode, pos, len);
>
> return status;
> }
> @@ -838,34 +837,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
> size_t copied, struct folio *folio)
> {
> const struct iomap *srcmap = iomap_iter_srcmap(iter);
> - loff_t old_size = iter->inode->i_size;
> - size_t ret;
> -
> - if (srcmap->type == IOMAP_INLINE) {
> - ret = iomap_write_end_inline(iter, folio, pos, copied);
> - } else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
> - ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
> - copied, &folio->page, NULL);
> - } else {
> - ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
> - }
>
> - /*
> - * Update the in-memory inode size after copying the data into the page
> - * cache. It's up to the file system to write the updated size to disk,
> - * preferably after I/O completion so that no stale data is exposed.
> - */
> - if (pos + ret > old_size) {
> - i_size_write(iter->inode, pos + ret);
> - iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
> - }
> - __iomap_put_folio(iter, pos, ret, folio);
> -
> - if (old_size < pos)
> - pagecache_isize_extended(iter->inode, old_size, pos);
> - if (ret < len)
> - iomap_write_failed(iter->inode, pos + ret, len - ret);
> - return ret;
> + if (srcmap->type == IOMAP_INLINE)
> + return iomap_write_end_inline(iter, folio, pos, copied);
> + if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
> + return block_write_end(NULL, iter->inode->i_mapping, pos, len,
> + copied, &folio->page, NULL);
> + return __iomap_write_end(iter->inode, pos, len, copied, folio);
> }
>
> static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> @@ -880,6 +858,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>
> do {
> struct folio *folio;
> + loff_t old_size;
> size_t offset; /* Offset into folio */
> size_t bytes; /* Bytes to write to folio */
> size_t copied; /* Bytes copied from user */
> @@ -912,8 +891,10 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> }
>
> status = iomap_write_begin(iter, pos, bytes, &folio);
> - if (unlikely(status))
> + if (unlikely(status)) {
> + iomap_write_failed(iter->inode, pos, bytes);
> break;
> + }
> if (iter->iomap.flags & IOMAP_F_STALE)
> break;
>
> @@ -927,6 +908,24 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
> status = iomap_write_end(iter, pos, bytes, copied, folio);
>
> + /*
> + * Update the in-memory inode size after copying the data into
> + * the page cache. It's up to the file system to write the
> + * updated size to disk, preferably after I/O completion so that
> + * no stale data is exposed.
> + */
> + old_size = iter->inode->i_size;
> + if (pos + status > old_size) {
> + i_size_write(iter->inode, pos + status);
> + iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
> + }
> + __iomap_put_folio(iter, pos, status, folio);
Why is it necessary to hoist the __iomap_put_folio calls from
iomap_write_end into iomap_write_iter, iomap_unshare_iter, and
iomap_zero_iter? None of those functions seem to use it, and it makes
more sense to me that iomap_write_end releases the folio that
iomap_write_begin returned.
--D
> +
> + if (old_size < pos)
> + pagecache_isize_extended(iter->inode, old_size, pos);
> + if (status < bytes)
> + iomap_write_failed(iter->inode, pos + status,
> + bytes - status);
> if (unlikely(copied != status))
> iov_iter_revert(i, copied - status);
>
> @@ -1296,6 +1295,7 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
> bytes = folio_size(folio) - offset;
>
> bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
> + __iomap_put_folio(iter, pos, bytes, folio);
> if (WARN_ON_ONCE(bytes == 0))
> return -EIO;
>
> @@ -1360,6 +1360,7 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
> folio_mark_accessed(folio);
>
> bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
> + __iomap_put_folio(iter, pos, bytes, folio);
> if (WARN_ON_ONCE(bytes == 0))
> return -EIO;
>
> --
> 2.39.2
>
>
On Mon, Mar 11, 2024 at 08:48:29AM -0700, Darrick J. Wong wrote:
> This change should be a separate patch with its own justification.
> Which is, AFAICT, something along the lines of:
>
> "Unsharing and zeroing can only happen within EOF, so there is never a
> need to perform posteof pagecache truncation if write begin fails."
Agreed.
> > Signed-off-by: Zhang Yi <[email protected]>
>
> Doesn't this patch fix a bug in ext4?
Only with the not yet merged ext4 conversion to iomap for buffered I/O,
which is not merged yet.
On 2024/3/11 23:48, Darrick J. Wong wrote:
> On Mon, Mar 11, 2024 at 08:22:54PM +0800, Zhang Yi wrote:
>> From: Zhang Yi <[email protected]>
>>
>> Increase i_size in iomap_zero_range() and iomap_unshare_iter() is not
>> needed, the caller should handle it. Especially, when truncate partial
>> block, we could not increase i_size beyond the new EOF here. It doesn't
>> affect xfs and gfs2 now because they set the new file size after zero
>> out, it doesn't matter that a transient increase in i_size, but it will
>> affect ext4 because it set file size before truncate.
>
>> At the same time,
>> iomap_write_failed() is also not needed for above two cases too, so
>> factor them out and move them to iomap_write_iter() and
>> iomap_zero_iter().
>
> This change should be a separate patch with its own justification.
> Which is, AFAICT, something along the lines of:
>
> "Unsharing and zeroing can only happen within EOF, so there is never a
> need to perform posteof pagecache truncation if write begin fails."
Sure.
>
>> Signed-off-by: Zhang Yi <[email protected]>
>
> Doesn't this patch fix a bug in ext4?
Yeah, the same as Christoph answered.
>
>> ---
>> fs/iomap/buffered-io.c | 59 +++++++++++++++++++++---------------------
>> 1 file changed, 30 insertions(+), 29 deletions(-)
>>
>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>> index 093c4515b22a..19f91324c690 100644
>> --- a/fs/iomap/buffered-io.c
>> +++ b/fs/iomap/buffered-io.c
>> @@ -786,7 +786,6 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
>>
>> out_unlock:
>> __iomap_put_folio(iter, pos, 0, folio);
>> - iomap_write_failed(iter->inode, pos, len);
>>
>> return status;
>> }
>> @@ -838,34 +837,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
>> size_t copied, struct folio *folio)
>> {
>> const struct iomap *srcmap = iomap_iter_srcmap(iter);
>> - loff_t old_size = iter->inode->i_size;
>> - size_t ret;
>> -
>> - if (srcmap->type == IOMAP_INLINE) {
>> - ret = iomap_write_end_inline(iter, folio, pos, copied);
>> - } else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
>> - ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
>> - copied, &folio->page, NULL);
>> - } else {
>> - ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
>> - }
>>
>> - /*
>> - * Update the in-memory inode size after copying the data into the page
>> - * cache. It's up to the file system to write the updated size to disk,
>> - * preferably after I/O completion so that no stale data is exposed.
>> - */
>> - if (pos + ret > old_size) {
>> - i_size_write(iter->inode, pos + ret);
>> - iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
>> - }
>> - __iomap_put_folio(iter, pos, ret, folio);
>> -
>> - if (old_size < pos)
>> - pagecache_isize_extended(iter->inode, old_size, pos);
>> - if (ret < len)
>> - iomap_write_failed(iter->inode, pos + ret, len - ret);
>> - return ret;
>> + if (srcmap->type == IOMAP_INLINE)
>> + return iomap_write_end_inline(iter, folio, pos, copied);
>> + if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
>> + return block_write_end(NULL, iter->inode->i_mapping, pos, len,
>> + copied, &folio->page, NULL);
>> + return __iomap_write_end(iter->inode, pos, len, copied, folio);
>> }
>>
>> static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>> @@ -880,6 +858,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>>
>> do {
>> struct folio *folio;
>> + loff_t old_size;
>> size_t offset; /* Offset into folio */
>> size_t bytes; /* Bytes to write to folio */
>> size_t copied; /* Bytes copied from user */
>> @@ -912,8 +891,10 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>> }
>>
>> status = iomap_write_begin(iter, pos, bytes, &folio);
>> - if (unlikely(status))
>> + if (unlikely(status)) {
>> + iomap_write_failed(iter->inode, pos, bytes);
>> break;
>> + }
>> if (iter->iomap.flags & IOMAP_F_STALE)
>> break;
>>
>> @@ -927,6 +908,24 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>> copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
>> status = iomap_write_end(iter, pos, bytes, copied, folio);
>>
>> + /*
>> + * Update the in-memory inode size after copying the data into
>> + * the page cache. It's up to the file system to write the
>> + * updated size to disk, preferably after I/O completion so that
>> + * no stale data is exposed.
>> + */
>> + old_size = iter->inode->i_size;
>> + if (pos + status > old_size) {
>> + i_size_write(iter->inode, pos + status);
>> + iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
>> + }
>> + __iomap_put_folio(iter, pos, status, folio);
>
> Why is it necessary to hoist the __iomap_put_folio calls from
> iomap_write_end into iomap_write_iter, iomap_unshare_iter, and
> iomap_zero_iter? None of those functions seem to use it, and it makes
> more sense to me that iomap_write_end releases the folio that
> iomap_write_begin returned.
>
Because we have to update i_size before __iomap_put_folio() in
iomap_write_iter(). If not, once we unlock folio, it could be raced
by the backgroud write back which could start writing back and call
folio_zero_segment() (please see iomap_writepage_handle_eof()) to
zero out the valid data beyond the not updated i_size. So we
have to move out __iomap_put_folio() out together with the i_size
updating.
Thanks,
Yi.
On Tue, Mar 12, 2024 at 08:59:15PM +0800, Zhang Yi wrote:
> On 2024/3/11 23:48, Darrick J. Wong wrote:
> > On Mon, Mar 11, 2024 at 08:22:54PM +0800, Zhang Yi wrote:
> >> From: Zhang Yi <[email protected]>
> >>
> >> Increase i_size in iomap_zero_range() and iomap_unshare_iter() is not
> >> needed, the caller should handle it. Especially, when truncate partial
> >> block, we could not increase i_size beyond the new EOF here. It doesn't
> >> affect xfs and gfs2 now because they set the new file size after zero
> >> out, it doesn't matter that a transient increase in i_size, but it will
> >> affect ext4 because it set file size before truncate.
> >
> >> At the same time,
> >> iomap_write_failed() is also not needed for above two cases too, so
> >> factor them out and move them to iomap_write_iter() and
> >> iomap_zero_iter().
> >
> > This change should be a separate patch with its own justification.
> > Which is, AFAICT, something along the lines of:
> >
> > "Unsharing and zeroing can only happen within EOF, so there is never a
> > need to perform posteof pagecache truncation if write begin fails."
>
> Sure.
>
> >
> >> Signed-off-by: Zhang Yi <[email protected]>
> >
> > Doesn't this patch fix a bug in ext4?
>
> Yeah, the same as Christoph answered.
>
> >
> >> ---
> >> fs/iomap/buffered-io.c | 59 +++++++++++++++++++++---------------------
> >> 1 file changed, 30 insertions(+), 29 deletions(-)
> >>
> >> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> >> index 093c4515b22a..19f91324c690 100644
> >> --- a/fs/iomap/buffered-io.c
> >> +++ b/fs/iomap/buffered-io.c
> >> @@ -786,7 +786,6 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
> >>
> >> out_unlock:
> >> __iomap_put_folio(iter, pos, 0, folio);
> >> - iomap_write_failed(iter->inode, pos, len);
> >>
> >> return status;
> >> }
> >> @@ -838,34 +837,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
> >> size_t copied, struct folio *folio)
> >> {
> >> const struct iomap *srcmap = iomap_iter_srcmap(iter);
> >> - loff_t old_size = iter->inode->i_size;
> >> - size_t ret;
> >> -
> >> - if (srcmap->type == IOMAP_INLINE) {
> >> - ret = iomap_write_end_inline(iter, folio, pos, copied);
> >> - } else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
> >> - ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
> >> - copied, &folio->page, NULL);
> >> - } else {
> >> - ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
> >> - }
> >>
> >> - /*
> >> - * Update the in-memory inode size after copying the data into the page
> >> - * cache. It's up to the file system to write the updated size to disk,
> >> - * preferably after I/O completion so that no stale data is exposed.
> >> - */
> >> - if (pos + ret > old_size) {
> >> - i_size_write(iter->inode, pos + ret);
> >> - iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
> >> - }
> >> - __iomap_put_folio(iter, pos, ret, folio);
> >> -
> >> - if (old_size < pos)
> >> - pagecache_isize_extended(iter->inode, old_size, pos);
> >> - if (ret < len)
> >> - iomap_write_failed(iter->inode, pos + ret, len - ret);
> >> - return ret;
> >> + if (srcmap->type == IOMAP_INLINE)
> >> + return iomap_write_end_inline(iter, folio, pos, copied);
> >> + if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
> >> + return block_write_end(NULL, iter->inode->i_mapping, pos, len,
> >> + copied, &folio->page, NULL);
> >> + return __iomap_write_end(iter->inode, pos, len, copied, folio);
> >> }
> >>
> >> static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> >> @@ -880,6 +858,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> >>
> >> do {
> >> struct folio *folio;
> >> + loff_t old_size;
> >> size_t offset; /* Offset into folio */
> >> size_t bytes; /* Bytes to write to folio */
> >> size_t copied; /* Bytes copied from user */
> >> @@ -912,8 +891,10 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> >> }
> >>
> >> status = iomap_write_begin(iter, pos, bytes, &folio);
> >> - if (unlikely(status))
> >> + if (unlikely(status)) {
> >> + iomap_write_failed(iter->inode, pos, bytes);
> >> break;
> >> + }
> >> if (iter->iomap.flags & IOMAP_F_STALE)
> >> break;
> >>
> >> @@ -927,6 +908,24 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> >> copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
> >> status = iomap_write_end(iter, pos, bytes, copied, folio);
> >>
> >> + /*
> >> + * Update the in-memory inode size after copying the data into
> >> + * the page cache. It's up to the file system to write the
> >> + * updated size to disk, preferably after I/O completion so that
> >> + * no stale data is exposed.
> >> + */
> >> + old_size = iter->inode->i_size;
> >> + if (pos + status > old_size) {
> >> + i_size_write(iter->inode, pos + status);
> >> + iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
> >> + }
> >> + __iomap_put_folio(iter, pos, status, folio);
> >
> > Why is it necessary to hoist the __iomap_put_folio calls from
> > iomap_write_end into iomap_write_iter, iomap_unshare_iter, and
> > iomap_zero_iter? None of those functions seem to use it, and it makes
> > more sense to me that iomap_write_end releases the folio that
> > iomap_write_begin returned.
> >
>
> Because we have to update i_size before __iomap_put_folio() in
> iomap_write_iter(). If not, once we unlock folio, it could be raced
> by the backgroud write back which could start writing back and call
> folio_zero_segment() (please see iomap_writepage_handle_eof()) to
> zero out the valid data beyond the not updated i_size. So we
> have to move out __iomap_put_folio() out together with the i_size
> updating.
Ahah. Please make a note of that in the comment for dunces like me.
/*
* Update the in-memory inode size after copying the data into
* the page cache. It's up to the file system to write the
* updated size to disk, preferably after I/O completion so that
* no stale data is exposed. Only once that's done can we
* unlock and release the folio.
*/
--D
> Thanks,
> Yi.
>
>
On 2024/3/13 0:24, Darrick J. Wong wrote:
> On Tue, Mar 12, 2024 at 08:59:15PM +0800, Zhang Yi wrote:
>> On 2024/3/11 23:48, Darrick J. Wong wrote:
>>> On Mon, Mar 11, 2024 at 08:22:54PM +0800, Zhang Yi wrote:
>>>> From: Zhang Yi <[email protected]>
>>>>
[...]
>>>> @@ -927,6 +908,24 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>>>> copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
>>>> status = iomap_write_end(iter, pos, bytes, copied, folio);
>>>>
>>>> + /*
>>>> + * Update the in-memory inode size after copying the data into
>>>> + * the page cache. It's up to the file system to write the
>>>> + * updated size to disk, preferably after I/O completion so that
>>>> + * no stale data is exposed.
>>>> + */
>>>> + old_size = iter->inode->i_size;
>>>> + if (pos + status > old_size) {
>>>> + i_size_write(iter->inode, pos + status);
>>>> + iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
>>>> + }
>>>> + __iomap_put_folio(iter, pos, status, folio);
>>>
>>> Why is it necessary to hoist the __iomap_put_folio calls from
>>> iomap_write_end into iomap_write_iter, iomap_unshare_iter, and
>>> iomap_zero_iter? None of those functions seem to use it, and it makes
>>> more sense to me that iomap_write_end releases the folio that
>>> iomap_write_begin returned.
>>>
>>
>> Because we have to update i_size before __iomap_put_folio() in
>> iomap_write_iter(). If not, once we unlock folio, it could be raced
>> by the backgroud write back which could start writing back and call
>> folio_zero_segment() (please see iomap_writepage_handle_eof()) to
>> zero out the valid data beyond the not updated i_size. So we
>> have to move out __iomap_put_folio() out together with the i_size
>> updating.
>
> Ahah. Please make a note of that in the comment for dunces like me.
>
> /*
> * Update the in-memory inode size after copying the data into
> * the page cache. It's up to the file system to write the
> * updated size to disk, preferably after I/O completion so that
> * no stale data is exposed. Only once that's done can we
> * unlock and release the folio.
> */
>
Sure.