Changing size of a file on server and local update (fuse_write_update_size)
should be always protected by inode->i_mutex. Otherwise a race like this is
possible:
1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
2. Process 'B' performs ordinary buffered write(2) with a length big enough
to extend the file beyond "offset + length" of fallocate call.
3. Process 'A' resumes execution of fuse_file_fallocate() and calls
fuse_write_update_size(inode, offset + length). But 'offset + length' was
obsoleted by write from previous step.
Signed-off-by: Maxim V. Patlasov <[email protected]>
---
fs/fuse/file.c | 10 ++++++----
1 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index e570081..8dfbf7d 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2470,14 +2470,16 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
.mode = mode
};
int err;
+ bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) ||
+ (mode & FALLOC_FL_PUNCH_HOLE);
if (fc->no_fallocate)
return -EOPNOTSUPP;
- if (mode & FALLOC_FL_PUNCH_HOLE) {
+ if (lock_inode)
mutex_lock(&inode->i_mutex);
+ if (mode & FALLOC_FL_PUNCH_HOLE)
fuse_set_nowrite(inode);
- }
req = fuse_get_req_nopages(fc);
if (IS_ERR(req)) {
@@ -2511,10 +2513,10 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
fuse_invalidate_attr(inode);
out:
- if (mode & FALLOC_FL_PUNCH_HOLE) {
+ if (mode & FALLOC_FL_PUNCH_HOLE)
fuse_release_nowrite(inode);
+ if (lock_inode)
mutex_unlock(&inode->i_mutex);
- }
return err;
}
On 06/11/2013 06:59 AM, Maxim Patlasov wrote:
> Changing size of a file on server and local update (fuse_write_update_size)
> should be always protected by inode->i_mutex. Otherwise a race like this is
> possible:
>
> 1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
> fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
> 2. Process 'B' performs ordinary buffered write(2) with a length big enough
> to extend the file beyond "offset + length" of fallocate call.
> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
> fuse_write_update_size(inode, offset + length). But 'offset + length' was
> obsoleted by write from previous step.
>
Hi Maxim,
Doesn't fuse_write_update_size() already handle this particular case by
only ever extending the size?
Brian
> Signed-off-by: Maxim V. Patlasov <[email protected]>
> ---
> fs/fuse/file.c | 10 ++++++----
> 1 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index e570081..8dfbf7d 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2470,14 +2470,16 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
> .mode = mode
> };
> int err;
> + bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) ||
> + (mode & FALLOC_FL_PUNCH_HOLE);
>
> if (fc->no_fallocate)
> return -EOPNOTSUPP;
>
> - if (mode & FALLOC_FL_PUNCH_HOLE) {
> + if (lock_inode)
> mutex_lock(&inode->i_mutex);
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> fuse_set_nowrite(inode);
> - }
>
> req = fuse_get_req_nopages(fc);
> if (IS_ERR(req)) {
> @@ -2511,10 +2513,10 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
> fuse_invalidate_attr(inode);
>
> out:
> - if (mode & FALLOC_FL_PUNCH_HOLE) {
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> fuse_release_nowrite(inode);
> + if (lock_inode)
> mutex_unlock(&inode->i_mutex);
> - }
>
> return err;
> }
>
On 6/12/13 4:40 AM, Brian Foster wrote:
> On 06/11/2013 06:59 AM, Maxim Patlasov wrote:
>> Changing size of a file on server and local update (fuse_write_update_size)
>> should be always protected by inode->i_mutex. Otherwise a race like this is
>> possible:
>>
>> 1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
>> fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
>> 2. Process 'B' performs ordinary buffered write(2) with a length big enough
>> to extend the file beyond "offset + length" of fallocate call.
>> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
>> fuse_write_update_size(inode, offset + length). But 'offset + length' was
>> obsoleted by write from previous step.
>>
>
> Hi Maxim,
>
> Doesn't fuse_write_update_size() already handle this particular case by
> only ever extending the size?
>
As you say, fuse_write_update_size() does seem to protect against the
case Maxim writes in the commit log.
However, there is still an issue with with truncate(shrinking_offset)
and fallocate(growing_offset,~FALLOC_FL_KEEP_SIZE) racing, and changing
inode size in opposing order between file server and in core ->i_size.
Therefore, grabbing i_mutex is making fallocate and truncate atomic
against each other.
I guess we just need an updated commit log, and same code change?
Avati
On 6/11/13 3:59 AM, Maxim Patlasov wrote:
> - if (mode & FALLOC_FL_PUNCH_HOLE) {
> + if (lock_inode)
> mutex_lock(&inode->i_mutex);
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> fuse_set_nowrite(inode);
> - }
Just for clarity, can you make the condition to check
FALLOC_FL_PUNCH_HOLE and call to fuse_set_nowrite() nested within the
larger if (lock_inode) { .. } block? fuse_set_nowrite() should not be
called without i_mutex acquired. The current style of calling
mutex_lock() and fuse_set_nowrite() in separate conditions can
potentially cause bugs in the future if they were to get re-ordered due
to some unrelated patch. Nesting them makes the relation more explicit
and clear.
Thanks,
Avati
Anand, Brian,
06/12/2013 11:04 PM, Anand Avati пишет:
> On 6/11/13 3:59 AM, Maxim Patlasov wrote:
>
>> - if (mode & FALLOC_FL_PUNCH_HOLE) {
>> + if (lock_inode)
>> mutex_lock(&inode->i_mutex);
>
>> + if (mode & FALLOC_FL_PUNCH_HOLE)
>> fuse_set_nowrite(inode);
>> - }
>
> Just for clarity, can you make the condition to check
> FALLOC_FL_PUNCH_HOLE and call to fuse_set_nowrite() nested within the
> larger if (lock_inode) { .. } block? fuse_set_nowrite() should not be
> called without i_mutex acquired. The current style of calling
> mutex_lock() and fuse_set_nowrite() in separate conditions can
> potentially cause bugs in the future if they were to get re-ordered
> due to some unrelated patch. Nesting them makes the relation more
> explicit and clear.
Thanks a lot for review. I'll post updated patch soon.
Thanks,
Maxim