[Devel] [PATCH 3/8] fuse: do not take fc->lock in fuse_request_send_background()
Pavel Butsykin
pbutsykin at virtuozzo.com
Tue Apr 23 12:45:22 MSK 2019
On 23.04.2019 12:35, Kirill Tkhai wrote:
> On 23.04.2019 12:33, Pavel Butsykin wrote:
>>
>>
>> On 23.04.2019 12:21, Kirill Tkhai wrote:
>>> On 23.04.2019 11:51, Pavel Butsykin wrote:
>>>>
>>>>
>>>> On 23.04.2019 11:40, Kirill Tkhai wrote:
>>>>> On 23.04.2019 11:36, Pavel Butsykin wrote:
>>>>>> On 23.04.2019 10:48, Kirill Tkhai wrote:
>>>>>>> On 23.04.2019 09:56, Pavel Butsykin wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 03.04.2019 18:37, Kirill Tkhai wrote:
>>>>>>>>> ms commit 63825b4e1da5
>>>>>>>>>
>>>>>>>>> Currently, we take fc->lock there only to check for fc->connected.
>>>>>>>>> But this flag is changed only on connection abort, which is very
>>>>>>>>> rare operation.
>>>>>>>>>
>>>>>>>>> So allow checking fc->connected under just fc->bg_lock and use this lock
>>>>>>>>> (as well as fc->lock) when resetting fc->connected.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>>>>>>>>> Signed-off-by: Miklos Szeredi <mszeredi at redhat.com>
>>>>>>>>> ---
>>>>>>>>> fs/fuse/dev.c | 73 +++++++++++++++++++++++++++---------------------------
>>>>>>>>> fs/fuse/file.c | 4 ++-
>>>>>>>>> fs/fuse/fuse_i.h | 3 +-
>>>>>>>>> 3 files changed, 41 insertions(+), 39 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>>>>>>>>> index 1ffc10ff18ba..1355f4a0a8e4 100644
>>>>>>>>> --- a/fs/fuse/dev.c
>>>>>>>>> +++ b/fs/fuse/dev.c
>>>>>>>>> @@ -598,69 +598,70 @@ void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
>>>>>>>>> }
>>>>>>>>> EXPORT_SYMBOL_GPL(fuse_request_send);
>>>>>>>>>
>>>>>>>>> -/*
>>>>>>>>> - * Called under fc->lock
>>>>>>>>> - *
>>>>>>>>> - * fc->connected must have been checked previously
>>>>>>>>> - */
>>>>>>>>> -void fuse_request_send_background_nocheck(struct fuse_conn *fc,
>>>>>>>>> - struct fuse_req *req)
>>>>>>>>> +bool fuse_request_queue_background(struct fuse_conn *fc, struct fuse_req *req)
>>>>>>>>> {
>>>>>>>>> struct fuse_iqueue *fiq = req->fiq;
>>>>>>>>> + bool queued = false;
>>>>>>>>>
>>>>>>>>> - BUG_ON(!test_bit(FR_BACKGROUND, &req->flags));
>>>>>>>>> -
>>>>>>>>> + WARN_ON(!test_bit(FR_BACKGROUND, &req->flags));
>>>>>>>>> if (!test_bit(FR_WAITING, &req->flags)) {
>>>>>>>>> __set_bit(FR_WAITING, &req->flags);
>>>>>>>>> atomic_inc(&fc->num_waiting);
>>>>>>>>> }
>>>>>>>>> __set_bit(FR_ISREPLY, &req->flags);
>>>>>>>>> spin_lock(&fc->bg_lock);
>>>>>>>>> - fc->num_background++;
>>>>>>>>> - if (fc->num_background == fc->max_background)
>>>>>>>>> - fc->blocked = 1;
>>>>>>>>> - if (fc->num_background == fc->congestion_threshold &&
>>>>>>>>> - fc->bdi_initialized) {
>>>>>>>>> - set_bdi_congested(&fc->bdi, BLK_RW_SYNC);
>>>>>>>>> - set_bdi_congested(&fc->bdi, BLK_RW_ASYNC);
>>>>>>>>> - }
>>>>>>>>> + if (likely(fc->connected)) {
>>>>>>>>> + fc->num_background++;
>>>>>>>>> + if (fc->num_background == fc->max_background)
>>>>>>>>> + fc->blocked = 1;
>>>>>>>>> + if (fc->num_background == fc->congestion_threshold && fc->sb) {
>>>>>>>>> + set_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);
>>>>>>>>> + set_bdi_congested(fc->sb->s_bdi, BLK_RW_ASYNC);
>>>>>>>>> + }
>>>>>>>>>
>>>>>>>>> - if (test_bit(FR_NONBLOCKING, &req->flags)) {
>>>>>>>>> - fc->active_background++;
>>>>>>>>> - spin_lock(&fiq->waitq.lock);
>>>>>>>>> - req->in.h.unique = fuse_get_unique(fiq);
>>>>>>>>> - queue_request(fiq, req);
>>>>>>>>> - spin_unlock(&fiq->waitq.lock);
>>>>>>>>> - goto unlock;
>>>>>>>>> - }
>>>>>>>>> + if (test_bit(FR_NONBLOCKING, &req->flags)) {
>>>>>>>>> + fc->active_background++;
>>>>>>>>> + spin_lock(&fiq->waitq.lock);
>>>>>>>>> + req->in.h.unique = fuse_get_unique(fiq);
>>>>>>>>> + queue_request(fiq, req);
>>>>>>>>> + spin_unlock(&fiq->waitq.lock);
>>>>>>>>> + queued = true;
>>>>>>>>> + goto unlock;
>>>>>>>>> + }
>>>>>>>>>
>>>>>>>>> - list_add_tail(&req->list, &fc->bg_queue);
>>>>>>>>> - flush_bg_queue(fc, fiq);
>>>>>>>>> + list_add_tail(&req->list, &fc->bg_queue);
>>>>>>>>> + flush_bg_queue(fc, fiq);
>>>>>>>>> + queued = true;
>>>>>>>>> + }
>>>>>>>>> unlock:
>>>>>>>>> spin_unlock(&fc->bg_lock);
>>>>>>>>> + return queued;
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
>>>>>>>>> {
>>>>>>>>> - BUG_ON(!req->end);
>>>>>>>>> + bool fail;
>>>>>>>>> + WARN_ON(!req->end);
>>>>>>>>>
>>>>>>>>> if (fc->kio.op && !fc->kio.op->req_send(fc, req, true, false))
>>>>>>>>> return;
>>>>>>>>>
>>>>>>>>> spin_lock(&fc->lock);
>>>>>>>>> - if (req->page_cache && req->ff &&
>>>>>>>>> - test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state)) {
>>>>>>>>> + fail = (req->page_cache && req->ff &&
>>>>>>>>> + test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state));
>>>>>>>>> + spin_unlock(&fc->lock);
>>>>>>>>> +
>>>>>>>>> + if (fail) {
>>>>>>>>> + /* FIXME */
>>>>>>>>
>>>>>>>> What needs to be fixed here?
>>>>>>>
>>>>>>> Commit aims to remove fc->lock from this function (and it's called "fuse: do not
>>>>>>> take fc->lock in fuse_request_send_background()). But FUSE_S_FAIL_IMMEDIATELY
>>>>>>> vstorage crutch is made under fc->lock, so the lock remains, and "FIXME" is there.
>>>>>>
>>>>>> There already fi->lock.
>>>>>>
>>>>>>> I think the lock is not needed, since the crutch's bit FUSE_S_FAIL_IMMEDIATELY
>>>>>>> is set under lock, but we do not need for all queued requests in fuse_invalidate_files()
>>>>>>> after the bit is set. So, I remain this logic, and you may decide whether you
>>>>>>> need the lock or not.
>>>>>>
>>>>>> Ok, Unfortunately loсk is needed here, but fc->bg_lock instead of
>>>>>> fc->lock to synchronize test_bit(FUSE_S_FAIL_IMMEDIATELY) and
>>>>>> fc->bg_queue. Possible race:
>>>>>>
>>>>> Your formatting lost all spaces.
>>>>>
>>>>
>>>> One more try:
>>>>
>>>> fuse_request_send_background():........................fuse_invalidate_files():
>>>> test_bit(FUSE_S_FAIL_IMMEDIATELY,.&ff->ff_state)
>>>> ........................................................spin_lock(&fi->lock);
>>>> ........................................................list_for_each_entry(ff,.&fi->rw_files,.rw_entry)
>>>> ..........................................................set_bit(FUSE_S_FAIL_IMMEDIATELY,.&ff->ff_state);
>>>> ........................................................spin_unlock(&fi->lock);
>>>>
>>>> ........................................................spin_lock(&fc->lock);
>>>>
>>>> ........................................................spin_lock(&fc->bg_lock);
>>>> ........................................................fuse_kill_requests(fc,.inode,.&fc->bg_queue);
>>>> ........................................................spin_unlock(&fc->bg_lock);
>>>>
>>>> fuse_request_queue_background():
>>>> spin_lock(&fc->bg_lock);
>>>> list_add_tail(&req->list,.&fc->bg_queue);
>>>> flush_bg_queue(fc,.fiq);
>>>> spin_unlock(&fc->bg_lock);
>>>>
>>>> ........................................................spin_unlock(&fc->lock);
>>>
>>> Yeah, but fc->lock is still *not needed*.
>>
>> I said - "loсk is needed here, but fc->bg_lock instead of fc->lock".
>>
>>> We may just move immediate checking logic into fuse_request_queue_background():
>>>
>>> fuse: do not take fc->lock in fuse_request_send_background() - fixup
>>>
>>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>>> ---
>>> fs/fuse/dev.c | 24 ++++++------------------
>>> 1 file changed, 6 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>>> index 1355f4a0a8e4..bfc792c9b5dd 100644
>>> --- a/fs/fuse/dev.c
>>> +++ b/fs/fuse/dev.c
>>> @@ -610,7 +610,10 @@ bool fuse_request_queue_background(struct fuse_conn *fc, struct fuse_req *req)
>>> }
>>> __set_bit(FR_ISREPLY, &req->flags);
>>> spin_lock(&fc->bg_lock);
>>> - if (likely(fc->connected)) {
>>> + if (unlikely(req->page_cache && req->ff &&
>>> + test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state)))
>>> + req->out.h.error = -EIO;
>>
>> There's another place where synchronization with FUSE_S_FAIL_IMMEDIATELY will
>> still be broken:
>> /* Called under fi->lock, may release and reacquire it */
>> static void fuse_send_writepage(struct fuse_conn *fc, struct fuse_req *req)
>> __releases(fi->lock)
>> __acquires(fi->lock)
>> {
>> ...
>> if (test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state)) {
>
> No, after immediate check is moved into fuse_request_queue_background(),
> everything is OK. We just need to remove this excess the check
> from fuse_send_writepage().
Only read requests have setted req->page_cache, so we'll just lose
FUSE_S_FAIL_IMMEDIATELY check in case we remove 'excess' the check.
What about this patch? (see attach)
>>> + else if (likely(fc->connected)) {
>>> fc->num_background++;
>>> if (fc->num_background == fc->max_background)
>>> fc->blocked = 1;
>>> @@ -640,29 +643,14 @@ bool fuse_request_queue_background(struct fuse_conn *fc, struct fuse_req *req)
>>>
>>> void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
>>> {
>>> - bool fail;
>>> WARN_ON(!req->end);
>>>
>>> if (fc->kio.op && !fc->kio.op->req_send(fc, req, true, false))
>>> return;
>>>
>>> - spin_lock(&fc->lock);
>>> - fail = (req->page_cache && req->ff &&
>>> - test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state));
>>> - spin_unlock(&fc->lock);
>>> -
>>> - if (fail) {
>>> - /* FIXME */
>>> - BUG_ON(req->in.h.opcode != FUSE_READ);
>>> - req->out.h.error = -EIO;
>>> - __clear_bit(FR_BACKGROUND, &req->flags);
>>> - __clear_bit(FR_PENDING, &req->flags);
>>
>> I'm not sure we can drop this stuff.
>>
>>> - request_end(fc, req);
>>> - return;
>>> - }
>>> -
>>> if (!fuse_request_queue_background(fc, req)) {
>>> - req->out.h.error = -ENOTCONN;
>>> + if (!req->out.h.error)
>>> + req->out.h.error = -ENOTCONN;
>>> req->end(fc, req);
>>> fuse_put_request(fc, req);
>>> }
>>>
>
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