2013-06-13 08:17:27

by Maxim Patlasov

Subject: [PATCH] fuse: hold i_mutex in fuse_file_fallocate() - v2

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' calls ftruncate(2) shrinking the file. fuse_do_setattr()
sends shrinking FUSE_SETATTR request to the server and updates local i_size
by i_size_write(inode, outarg.attr.size).
3. Process 'A' resumes execution of fuse_file_fallocate() and calls
fuse_write_update_size(inode, offset + length). But 'offset + length' was
obsoleted by ftruncate from previous step.

Changed in v2 (thanks Brian and Anand for suggestions):
- made relation between mutex_lock() and fuse_set_nowrite(inode) more
explicit and clear.
- updated patch description to use ftruncate(2) in example

Signed-off-by: Maxim V. Patlasov <[email protected]>
---
fs/fuse/file.c | 12 ++++++++----
1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index e570081..35f2810 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2470,13 +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);
- fuse_set_nowrite(inode);
+ if (mode & FALLOC_FL_PUNCH_HOLE)
+ fuse_set_nowrite(inode);
}

req = fuse_get_req_nopages(fc);
@@ -2511,8 +2514,9 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
fuse_invalidate_attr(inode);

out:
- if (mode & FALLOC_FL_PUNCH_HOLE) {
- fuse_release_nowrite(inode);
+ if (lock_inode) {
+ if (mode & FALLOC_FL_PUNCH_HOLE)
+ fuse_release_nowrite(inode);
mutex_unlock(&inode->i_mutex);
}

2013-06-13 11:49:12

by Brian Foster

Subject: Re: [PATCH] fuse: hold i_mutex in fuse_file_fallocate() - v2

On 06/13/2013 04:16 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' calls ftruncate(2) shrinking the file. fuse_do_setattr()
> sends shrinking FUSE_SETATTR request to the server and updates local i_size
> by i_size_write(inode, outarg.attr.size).
> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
> fuse_write_update_size(inode, offset + length). But 'offset + length' was
> obsoleted by ftruncate from previous step.
>
> Changed in v2 (thanks Brian and Anand for suggestions):
> - made relation between mutex_lock() and fuse_set_nowrite(inode) more
> explicit and clear.
> - updated patch description to use ftruncate(2) in example
>
> Signed-off-by: Maxim V. Patlasov <[email protected]>
> ---

Makes more sense and I like the cleanup... thanks.

Reviewed-by: Brian Foster <[email protected]>

> fs/fuse/file.c | 12 ++++++++----
> 1 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index e570081..35f2810 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2470,13 +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);
> - fuse_set_nowrite(inode);
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> + fuse_set_nowrite(inode);
> }
>
> req = fuse_get_req_nopages(fc);
> @@ -2511,8 +2514,9 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
> fuse_invalidate_attr(inode);
>
> out:
> - if (mode & FALLOC_FL_PUNCH_HOLE) {
> - fuse_release_nowrite(inode);
> + if (lock_inode) {
> + if (mode & FALLOC_FL_PUNCH_HOLE)
> + fuse_release_nowrite(inode);
> mutex_unlock(&inode->i_mutex);
> }
>
>

2013-06-17 23:49:31

by Miklos Szeredi

Subject: Re: [PATCH] fuse: hold i_mutex in fuse_file_fallocate() - v2

On Thu, Jun 13, 2013 at 1:46 PM, Brian Foster <[email protected]> wrote:
> On 06/13/2013 04:16 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' calls ftruncate(2) shrinking the file. fuse_do_setattr()
>> sends shrinking FUSE_SETATTR request to the server and updates local i_size
>> by i_size_write(inode, outarg.attr.size).
>> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
>> fuse_write_update_size(inode, offset + length). But 'offset + length' was
>> obsoleted by ftruncate from previous step.
>>
>> Changed in v2 (thanks Brian and Anand for suggestions):
>> - made relation between mutex_lock() and fuse_set_nowrite(inode) more
>> explicit and clear.
>> - updated patch description to use ftruncate(2) in example
>>
>> Signed-off-by: Maxim V. Patlasov <[email protected]>

Thanks, applied.

Miklos