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SubjectRe: [PATCH 1/2] netfs: release the folio lock and put the folio before retrying
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On 7/1/22 6:38 PM, Jeff Layton wrote:
> On Fri, 2022-07-01 at 10:29 +0800, xiubli@redhat.com wrote:
>> From: Xiubo Li <xiubli@redhat.com>
>>
>> The lower layer filesystem should always make sure the folio is
>> locked and do the unlock and put the folio in netfs layer.
>>
>> URL: https://tracker.ceph.com/issues/56423
>> Signed-off-by: Xiubo Li <xiubli@redhat.com>
>> ---
>> fs/netfs/buffered_read.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
>> index 42f892c5712e..257fd37c2461 100644
>> --- a/fs/netfs/buffered_read.c
>> +++ b/fs/netfs/buffered_read.c
>> @@ -351,8 +351,11 @@ int netfs_write_begin(struct netfs_inode *ctx,
>> ret = ctx->ops->check_write_begin(file, pos, len, folio, _fsdata);
>> if (ret < 0) {
>> trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
>> - if (ret == -EAGAIN)
>> + if (ret == -EAGAIN) {
>> + folio_unlock(folio);
>> + folio_put(folio);
>> goto retry;
>> + }
>> goto error;
>> }
>> }
> I don't know here... I think it might be better to just expect that when
> this function returns an error that the folio has already been unlocked.
> Doing it this way will mean that you will lock and unlock the folio a
> second time for no reason.
>
> Maybe something like this instead?
>
> diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
> index 42f892c5712e..8ae7b0f4c909 100644
> --- a/fs/netfs/buffered_read.c
> +++ b/fs/netfs/buffered_read.c
> @@ -353,7 +353,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
> trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
> if (ret == -EAGAIN)
> goto retry;
> - goto error;
> + goto error_unlocked;
> }
> }
>
> @@ -418,6 +418,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
> error:
> folio_unlock(folio);
> folio_put(folio);
> +error_unlocked:
> _leave(" = %d", ret);
> return ret;
> }

Then the "afs" won't work correctly:

377 static int afs_check_write_begin(struct file *file, loff_t pos,
unsigned len,
378                                  struct folio *folio, void **_fsdata)
379 {
380         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
381
382         return test_bit(AFS_VNODE_DELETED, &vnode->flags) ? -ESTALE : 0;
383 }

The "afs" does nothing with the folio lock.

-- Xiubo


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