Following process makes i_disksize exceed i_size:
generic_perform_write
copied = iov_iter_copy_from_user_atomic(len) // copied < len
ext4_da_write_end
| ext4_update_i_disksize
| new_i_size = pos + copied;
| WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
| generic_write_end
| copied = block_write_end(copied, len) // copied = 0
| if (unlikely(copied < len))
| if (!PageUptodate(page))
| copied = 0;
| if (pos + copied > inode->i_size) // return false
if (unlikely(copied == 0))
goto again;
if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
status = -EFAULT;
break;
}
We get i_disksize greater than i_size here, which could trigger WARNING
check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
ext4_dio_write_iter
iomap_dio_rw
__iomap_dio_rw // return err, length is not aligned to 512
ext4_handle_inode_extension
WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
RIP: 0010:ext4_file_write_iter+0xbc7
Call Trace:
vfs_write+0x3b1
ksys_write+0x77
do_syscall_64+0x39
Fix it by putting block_write_end() before i_disksize updating just
like ext4_write_end() does.
Fetch a reproducer in [Link].
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
Fixes: 64769240bd07f ("ext4: Add delayed allocation support in data=writeback mode")
Signed-off-by: Zhihao Cheng <[email protected]>
---
fs/ext4/inode.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf0b7dea4900..577dc23f3b78 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3136,6 +3136,8 @@ static int ext4_da_write_end(struct file *file,
loff_t new_i_size;
unsigned long start, end;
int write_mode = (int)(unsigned long)fsdata;
+ bool i_size_changed = false;
+ loff_t old_size = inode->i_size;
if (write_mode == FALL_BACK_TO_NONDELALLOC)
return ext4_write_end(file, mapping, pos,
@@ -3148,6 +3150,8 @@ static int ext4_da_write_end(struct file *file,
ext4_has_inline_data(inode))
return ext4_write_inline_data_end(inode, pos, len, copied, page);
+ copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
+
start = pos & (PAGE_SIZE - 1);
end = start + copied - 1;
@@ -3162,16 +3166,30 @@ static int ext4_da_write_end(struct file *file,
* check), we need to update i_disksize here as neither
* ext4_writepage() nor certain ext4_writepages() paths not
* allocating blocks update i_disksize.
- *
- * Note that we defer inode dirtying to generic_write_end() /
- * ext4_da_write_inline_data_end().
*/
new_i_size = pos + copied;
- if (copied && new_i_size > inode->i_size &&
- ext4_da_should_update_i_disksize(page, end))
- ext4_update_i_disksize(inode, new_i_size);
+ if (new_i_size > inode->i_size) {
+ i_size_write(inode, new_i_size);
+ i_size_changed = true;
+ if (copied && ext4_da_should_update_i_disksize(page, end))
+ ext4_update_i_disksize(inode, new_i_size);
+ }
+
+ unlock_page(page);
+ put_page(page);
+
+ if (old_size < pos)
+ pagecache_isize_extended(inode, old_size, pos);
+ /*
+ * Don't mark the inode dirty under page lock. First, it unnecessarily
+ * makes the holding time of page lock longer. Second, it forces lock
+ * ordering of page lock and transaction start for journaling
+ * filesystems.
+ */
+ if (i_size_changed)
+ mark_inode_dirty(inode);
- return generic_write_end(file, mapping, pos, len, copied, page, fsdata);
+ return copied;
}
/*
--
2.31.1
On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
> Following process makes i_disksize exceed i_size:
>
> generic_perform_write
> copied = iov_iter_copy_from_user_atomic(len) // copied < len
> ext4_da_write_end
> | ext4_update_i_disksize
> | new_i_size = pos + copied;
> | WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
> | generic_write_end
> | copied = block_write_end(copied, len) // copied = 0
> | if (unlikely(copied < len))
> | if (!PageUptodate(page))
> | copied = 0;
> | if (pos + copied > inode->i_size) // return false
> if (unlikely(copied == 0))
> goto again;
> if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
> status = -EFAULT;
> break;
> }
>
> We get i_disksize greater than i_size here, which could trigger WARNING
> check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
>
> ext4_dio_write_iter
> iomap_dio_rw
> __iomap_dio_rw // return err, length is not aligned to 512
> ext4_handle_inode_extension
> WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
>
> WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
> CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
> RIP: 0010:ext4_file_write_iter+0xbc7
> Call Trace:
> vfs_write+0x3b1
> ksys_write+0x77
> do_syscall_64+0x39
>
> Fix it by putting block_write_end() before i_disksize updating just
> like ext4_write_end() does.
>
> Fetch a reproducer in [Link].
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
> Fixes: 64769240bd07f ("ext4: Add delayed allocation support in data=writeback mode")
> Signed-off-by: Zhihao Cheng <[email protected]>
Good catch (although practically this will hardly have any negative
effect). But rather than opencoding generic_write_end() I'd do:
if (unlikely(copied < len) && !PageUptodate(page))
copied = 0;
at the beginning of ext4_da_write_end() and that should solve these
problems as well?
Honza
> ---
> fs/ext4/inode.c | 32 +++++++++++++++++++++++++-------
> 1 file changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index bf0b7dea4900..577dc23f3b78 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3136,6 +3136,8 @@ static int ext4_da_write_end(struct file *file,
> loff_t new_i_size;
> unsigned long start, end;
> int write_mode = (int)(unsigned long)fsdata;
> + bool i_size_changed = false;
> + loff_t old_size = inode->i_size;
>
> if (write_mode == FALL_BACK_TO_NONDELALLOC)
> return ext4_write_end(file, mapping, pos,
> @@ -3148,6 +3150,8 @@ static int ext4_da_write_end(struct file *file,
> ext4_has_inline_data(inode))
> return ext4_write_inline_data_end(inode, pos, len, copied, page);
>
> + copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
> +
> start = pos & (PAGE_SIZE - 1);
> end = start + copied - 1;
>
> @@ -3162,16 +3166,30 @@ static int ext4_da_write_end(struct file *file,
> * check), we need to update i_disksize here as neither
> * ext4_writepage() nor certain ext4_writepages() paths not
> * allocating blocks update i_disksize.
> - *
> - * Note that we defer inode dirtying to generic_write_end() /
> - * ext4_da_write_inline_data_end().
> */
> new_i_size = pos + copied;
> - if (copied && new_i_size > inode->i_size &&
> - ext4_da_should_update_i_disksize(page, end))
> - ext4_update_i_disksize(inode, new_i_size);
> + if (new_i_size > inode->i_size) {
> + i_size_write(inode, new_i_size);
> + i_size_changed = true;
> + if (copied && ext4_da_should_update_i_disksize(page, end))
> + ext4_update_i_disksize(inode, new_i_size);
> + }
> +
> + unlock_page(page);
> + put_page(page);
> +
> + if (old_size < pos)
> + pagecache_isize_extended(inode, old_size, pos);
> + /*
> + * Don't mark the inode dirty under page lock. First, it unnecessarily
> + * makes the holding time of page lock longer. Second, it forces lock
> + * ordering of page lock and transaction start for journaling
> + * filesystems.
> + */
> + if (i_size_changed)
> + mark_inode_dirty(inode);
>
> - return generic_write_end(file, mapping, pos, len, copied, page, fsdata);
> + return copied;
> }
>
> /*
> --
> 2.31.1
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
Hi, Jan
> On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
>> Following process makes i_disksize exceed i_size:
>>
>> generic_perform_write
>> copied = iov_iter_copy_from_user_atomic(len) // copied < len
>> ext4_da_write_end
>> | ext4_update_i_disksize
>> | new_i_size = pos + copied;
>> | WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
>> | generic_write_end
>> | copied = block_write_end(copied, len) // copied = 0
>> | if (unlikely(copied < len))
>> | if (!PageUptodate(page))
>> | copied = 0;
>> | if (pos + copied > inode->i_size) // return false
>> if (unlikely(copied == 0))
>> goto again;
>> if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
>> status = -EFAULT;
>> break;
>> }
>>
>> We get i_disksize greater than i_size here, which could trigger WARNING
>> check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
>>
>> ext4_dio_write_iter
>> iomap_dio_rw
>> __iomap_dio_rw // return err, length is not aligned to 512
>> ext4_handle_inode_extension
>> WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
>>
>> WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
>> CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
>> RIP: 0010:ext4_file_write_iter+0xbc7
>> Call Trace:
>> vfs_write+0x3b1
>> ksys_write+0x77
>> do_syscall_64+0x39
>>
>> Fix it by putting block_write_end() before i_disksize updating just
>> like ext4_write_end() does.
>>
>> Fetch a reproducer in [Link].
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
>> Fixes: 64769240bd07f ("ext4: Add delayed allocation support in data=writeback mode")
>> Signed-off-by: Zhihao Cheng <[email protected]>
>
> Good catch (although practically this will hardly have any negative
> effect). But rather than opencoding generic_write_end() I'd do:
>
> if (unlikely(copied < len) && !PageUptodate(page))
> copied = 0;
>
> at the beginning of ext4_da_write_end() and that should solve these
> problems as well?
>
Yes, your suggestion looks good, and I think we can put the checking
just after ext4_write_inline_data_end(Line 3150)? On the one hand, we
can pass original 'copied' value in trace_ext4_da_write_end(), one the
other hand, ext4_write_inline_data_end() already has this checking.
> Hi, Jan
>> On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
>>> Following process makes i_disksize exceed i_size:
>>>
>>> generic_perform_write
>>> copied = iov_iter_copy_from_user_atomic(len) // copied < len
>>> ext4_da_write_end
>>> | ext4_update_i_disksize
>>> | new_i_size = pos + copied;
>>> | WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
>>> | generic_write_end
>>> | copied = block_write_end(copied, len) // copied = 0
>>> | if (unlikely(copied < len))
>>> | if (!PageUptodate(page))
>>> | copied = 0;
>>> | if (pos + copied > inode->i_size) // return false
>>> if (unlikely(copied == 0))
>>> goto again;
>>> if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
>>> status = -EFAULT;
>>> break;
>>> }
>>>
>>> We get i_disksize greater than i_size here, which could trigger WARNING
>>> check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
>>>
>>> ext4_dio_write_iter
>>> iomap_dio_rw
>>> __iomap_dio_rw // return err, length is not aligned to 512
>>> ext4_handle_inode_extension
>>> WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
>>>
>>> WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
>>> CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
>>> RIP: 0010:ext4_file_write_iter+0xbc7
>>> Call Trace:
>>> vfs_write+0x3b1
>>> ksys_write+0x77
>>> do_syscall_64+0x39
>>>
>>> Fix it by putting block_write_end() before i_disksize updating just
>>> like ext4_write_end() does.
>>>
>>> Fetch a reproducer in [Link].
>>>
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
>>> Fixes: 64769240bd07f ("ext4: Add delayed allocation support in
>>> data=writeback mode")
>>> Signed-off-by: Zhihao Cheng <[email protected]>
>>
>> Good catch (although practically this will hardly have any negative
>> effect). But rather than opencoding generic_write_end() I'd do:
>>
>> if (unlikely(copied < len) && !PageUptodate(page))
>> copied = 0;
>>
>> at the beginning of ext4_da_write_end() and that should solve these
>> problems as well?
>>
>
> Yes, your suggestion looks good, and I think we can put the checking
> just after ext4_write_inline_data_end(Line 3150)? On the one hand, we
> can pass original 'copied' value in trace_ext4_da_write_end(), one the
> other hand, ext4_write_inline_data_end() already has this checking.
> .
BTW, I want send another patch as follows:
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf0b7dea4900..570a687ae847 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
return ext4_write_inline_data_end(inode, pos, len,
copied, page);
start = pos & (PAGE_SIZE - 1);
- end = start + copied - 1;
+ end = start + (copied ? copied - 1 : copied);
/*
* Since we are holding inode lock, we are sure i_disksize <=
@@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
* ext4_da_write_inline_data_end().
*/
new_i_size = pos + copied;
- if (copied && new_i_size > inode->i_size &&
+ if (new_i_size > inode->i_size &&
ext4_da_should_update_i_disksize(page, end))
ext4_update_i_disksize(inode, new_i_size);
This modification handle unconsistent i_size and i_disksize imported by
ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
Paritially written may display a fake inode size for user, for example:
i_disksize=1
generic_perform_write
copied = iov_iter_copy_from_user_atomic(len) // copied = 0
ext4_da_write_end // skip updating i_disksize
generic_write_end
if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
i_size_write(inode, pos + copied); // i_size = 10
}
0 1 10 4096
|_|_______|_________..._____|
| |
i_size pos
Now, user see the i_size is 10 (i_disksize is still 1). After inode
destroyed, user will get the i_size is 1 read from disk.
On Sat 18-03-23 16:51:00, Zhihao Cheng wrote:
> > Hi, Jan
> > > On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
> > > > Following process makes i_disksize exceed i_size:
> > > >
> > > > generic_perform_write
> > > > ? copied = iov_iter_copy_from_user_atomic(len) // copied < len
> > > > ? ext4_da_write_end
> > > > ? | ext4_update_i_disksize
> > > > ? |? new_i_size = pos + copied;
> > > > ? |? WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
> > > > ? | generic_write_end
> > > > ? |? copied = block_write_end(copied, len) // copied = 0
> > > > ? |?? if (unlikely(copied < len))
> > > > ? |??? if (!PageUptodate(page))
> > > > ? |???? copied = 0;
> > > > ? |? if (pos + copied > inode->i_size) // return false
> > > > ? if (unlikely(copied == 0))
> > > > ?? goto again;
> > > > ? if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
> > > > ?? status = -EFAULT;
> > > > ?? break;
> > > > ? }
> > > >
> > > > We get i_disksize greater than i_size here, which could trigger WARNING
> > > > check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
> > > >
> > > > ext4_dio_write_iter
> > > > ? iomap_dio_rw
> > > > ?? __iomap_dio_rw // return err, length is not aligned to 512
> > > > ? ext4_handle_inode_extension
> > > > ?? WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
> > > >
> > > > ? WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
> > > > ? CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
> > > > ? RIP: 0010:ext4_file_write_iter+0xbc7
> > > > ? Call Trace:
> > > > ?? vfs_write+0x3b1
> > > > ?? ksys_write+0x77
> > > > ?? do_syscall_64+0x39
> > > >
> > > > Fix it by putting block_write_end() before i_disksize updating just
> > > > like ext4_write_end() does.
> > > >
> > > > Fetch a reproducer in [Link].
> > > >
> > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
> > > > Fixes: 64769240bd07f ("ext4: Add delayed allocation support in
> > > > data=writeback mode")
> > > > Signed-off-by: Zhihao Cheng <[email protected]>
> > >
> > > Good catch (although practically this will hardly have any negative
> > > effect). But rather than opencoding generic_write_end() I'd do:
> > >
> > > ???????? if (unlikely(copied < len) && !PageUptodate(page))
> > > ???????????????? copied = 0;
> > >
> > > at the beginning of ext4_da_write_end() and that should solve these
> > > problems as well?
> > >
> >
> > Yes, your suggestion looks good, and I think we can put the checking
> > just after ext4_write_inline_data_end(Line 3150)? On the one hand, we
> > can pass original 'copied' value in trace_ext4_da_write_end(), one the
> > other hand, ext4_write_inline_data_end() already has this checking.
> > .
>
> BTW, I want send another patch as follows:
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index bf0b7dea4900..570a687ae847 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
> return ext4_write_inline_data_end(inode, pos, len, copied,
> page);
>
> start = pos & (PAGE_SIZE - 1);
> - end = start + copied - 1;
> + end = start + (copied ? copied - 1 : copied);
>
> /*
> * Since we are holding inode lock, we are sure i_disksize <=
> @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
> * ext4_da_write_inline_data_end().
> */
> new_i_size = pos + copied;
> - if (copied && new_i_size > inode->i_size &&
> + if (new_i_size > inode->i_size &&
> ext4_da_should_update_i_disksize(page, end))
> ext4_update_i_disksize(inode, new_i_size);
>
> This modification handle unconsistent i_size and i_disksize imported by
> ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
>
> Paritially written may display a fake inode size for user, for example:
>
>
>
> i_disksize=1
>
> generic_perform_write
>
> copied = iov_iter_copy_from_user_atomic(len) // copied = 0
>
> ext4_da_write_end // skip updating i_disksize
>
> generic_write_end
>
> if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
>
> i_size_write(inode, pos + copied); // i_size = 10
>
> }
>
>
>
> 0 1 10 4096
>
> |_|_______|_________..._____|
>
> | |
>
> i_size pos
>
>
>
> Now, user see the i_size is 10 (i_disksize is still 1). After inode
>
> destroyed, user will get the i_size is 1 read from disk.
OK, but shouldn't we rather change generic_write_end() to not increase
i_size if no write happened? Because that is what seems somewhat
problematic...
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
[...]
>> BTW, I want send another patch as follows:
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index bf0b7dea4900..570a687ae847 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
>> return ext4_write_inline_data_end(inode, pos, len, copied,
>> page);
>>
>> start = pos & (PAGE_SIZE - 1);
>> - end = start + copied - 1;
>> + end = start + (copied ? copied - 1 : copied);
>>
>> /*
>> * Since we are holding inode lock, we are sure i_disksize <=
>> @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
>> * ext4_da_write_inline_data_end().
>> */
>> new_i_size = pos + copied;
>> - if (copied && new_i_size > inode->i_size &&
>> + if (new_i_size > inode->i_size &&
>> ext4_da_should_update_i_disksize(page, end))
>> ext4_update_i_disksize(inode, new_i_size);
>>
>> This modification handle unconsistent i_size and i_disksize imported by
>> ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
>>
>> Paritially written may display a fake inode size for user, for example:
>>
>>
>>
>> i_disksize=1
>>
>> generic_perform_write
>>
>> copied = iov_iter_copy_from_user_atomic(len) // copied = 0
>>
>> ext4_da_write_end // skip updating i_disksize
>>
>> generic_write_end
>>
>> if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
>>
>> i_size_write(inode, pos + copied); // i_size = 10
>>
>> }
>>
>>
>>
>> 0 1 10 4096
>>
>> |_|_______|_________..._____|
>>
>> | |
>>
>> i_size pos
>>
>>
>>
>> Now, user see the i_size is 10 (i_disksize is still 1). After inode
>>
>> destroyed, user will get the i_size is 1 read from disk.
>
> OK, but shouldn't we rather change generic_write_end() to not increase
> i_size if no write happened? Because that is what seems somewhat
> problematic...
>
> Honza
>
After looking through some code, I find some other places have similar
problem:
1. In ext4_write_end(), i_size is updated by ext4 not generic_write_end().
2. The iommap framework, i_size is updated even copied is zero.
3. ubifs_write_end, i_size is updated even copied is zero.
It seems that fixing all places is not an easy work.
On Mon 20-03-23 20:49:07, Zhihao Cheng wrote:
> [...]
>
> > > BTW, I want send another patch as follows:
> > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > > index bf0b7dea4900..570a687ae847 100644
> > > --- a/fs/ext4/inode.c
> > > +++ b/fs/ext4/inode.c
> > > @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
> > > return ext4_write_inline_data_end(inode, pos, len, copied,
> > > page);
> > >
> > > start = pos & (PAGE_SIZE - 1);
> > > - end = start + copied - 1;
> > > + end = start + (copied ? copied - 1 : copied);
> > >
> > > /*
> > > * Since we are holding inode lock, we are sure i_disksize <=
> > > @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
> > > * ext4_da_write_inline_data_end().
> > > */
> > > new_i_size = pos + copied;
> > > - if (copied && new_i_size > inode->i_size &&
> > > + if (new_i_size > inode->i_size &&
> > > ext4_da_should_update_i_disksize(page, end))
> > > ext4_update_i_disksize(inode, new_i_size);
> > >
> > > This modification handle unconsistent i_size and i_disksize imported by
> > > ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
> > >
> > > Paritially written may display a fake inode size for user, for example:
> > >
> > >
> > >
> > > i_disksize=1
> > >
> > > generic_perform_write
> > >
> > > copied = iov_iter_copy_from_user_atomic(len) // copied = 0
> > >
> > > ext4_da_write_end // skip updating i_disksize
> > >
> > > generic_write_end
> > >
> > > if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
> > >
> > > i_size_write(inode, pos + copied); // i_size = 10
> > >
> > > }
> > >
> > >
> > >
> > > 0 1 10 4096
> > >
> > > |_|_______|_________..._____|
> > >
> > > | |
> > >
> > > i_size pos
> > >
> > >
> > >
> > > Now, user see the i_size is 10 (i_disksize is still 1). After inode
> > >
> > > destroyed, user will get the i_size is 1 read from disk.
> >
> > OK, but shouldn't we rather change generic_write_end() to not increase
> > i_size if no write happened? Because that is what seems somewhat
> > problematic...
> >
> > Honza
> >
>
> After looking through some code, I find some other places have similar
> problem:
> 1. In ext4_write_end(), i_size is updated by ext4 not generic_write_end().
> 2. The iommap framework, i_size is updated even copied is zero.
> 3. ubifs_write_end, i_size is updated even copied is zero.
>
> It seems that fixing all places is not an easy work.
Well, yeah, probably not trivial but still desirable ;). Will you look into
that?
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
> On Mon 20-03-23 20:49:07, Zhihao Cheng wrote:
>> [...]
>>
>>>> BTW, I want send another patch as follows:
>>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>>> index bf0b7dea4900..570a687ae847 100644
>>>> --- a/fs/ext4/inode.c
>>>> +++ b/fs/ext4/inode.c
>>>> @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
>>>> return ext4_write_inline_data_end(inode, pos, len, copied,
>>>> page);
>>>>
>>>> start = pos & (PAGE_SIZE - 1);
>>>> - end = start + copied - 1;
>>>> + end = start + (copied ? copied - 1 : copied);
>>>>
>>>> /*
>>>> * Since we are holding inode lock, we are sure i_disksize <=
>>>> @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
>>>> * ext4_da_write_inline_data_end().
>>>> */
>>>> new_i_size = pos + copied;
>>>> - if (copied && new_i_size > inode->i_size &&
>>>> + if (new_i_size > inode->i_size &&
>>>> ext4_da_should_update_i_disksize(page, end))
>>>> ext4_update_i_disksize(inode, new_i_size);
>>>>
>>>> This modification handle unconsistent i_size and i_disksize imported by
>>>> ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
>>>>
>>>> Paritially written may display a fake inode size for user, for example:
>>>>
>>>>
>>>>
>>>> i_disksize=1
>>>>
>>>> generic_perform_write
>>>>
>>>> copied = iov_iter_copy_from_user_atomic(len) // copied = 0
>>>>
>>>> ext4_da_write_end // skip updating i_disksize
>>>>
>>>> generic_write_end
>>>>
>>>> if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
>>>>
>>>> i_size_write(inode, pos + copied); // i_size = 10
>>>>
>>>> }
>>>>
>>>>
>>>>
>>>> 0 1 10 4096
>>>>
>>>> |_|_______|_________..._____|
>>>>
>>>> | |
>>>>
>>>> i_size pos
>>>>
>>>>
>>>>
>>>> Now, user see the i_size is 10 (i_disksize is still 1). After inode
>>>>
>>>> destroyed, user will get the i_size is 1 read from disk.
>>>
>>> OK, but shouldn't we rather change generic_write_end() to not increase
>>> i_size if no write happened? Because that is what seems somewhat
>>> problematic...
>>>
>>> Honza
>>>
>>
>> After looking through some code, I find some other places have similar
>> problem:
>> 1. In ext4_write_end(), i_size is updated by ext4 not generic_write_end().
>> 2. The iommap framework, i_size is updated even copied is zero.
>> 3. ubifs_write_end, i_size is updated even copied is zero.
>>
>> It seems that fixing all places is not an easy work.
>
> Well, yeah, probably not trivial but still desirable ;). Will you look into
> that?
>
> Honza
>
I'am happy to investigate it, maybe it will take some time, and I'm also
glad to help review code if somebody come up a solution firstly.