On 17.10.2018 16:57, Kirill Tkhai wrote:
> request_end() takes fc->lock, so we in case of error we bump
> into deadlock:
>
> Call Trace:
> [<ffffffffb3bb63f5>] _raw_spin_lock+0x75/0xc0
> [<ffffffffc170871b>] spin_lock+0x18/0x1b [fuse]
> [<ffffffffc170ba63>] request_end+0x265/0x72b [fuse]
> [<ffffffffc18a1b8d>] pcs_fuse_submit+0x9fb/0xaa3 [fuse_kio_pcs]
> [<ffffffffc18a35c4>] kpcs_req_send+0x793/0xa60 [fuse_kio_pcs]
> [<ffffffffc170b6ca>] flush_bg_queue+0x14f/0x283 [fuse]
> [<ffffffffc170d4d4>] fuse_request_send_background_locked+0x50b/0x512 [fuse]
> [<ffffffffc170d844>] fuse_request_send_background+0x369/0x43f [fuse]
> [<ffffffffc173028b>] fuse_send_readpages+0x372/0x3b5 [fuse]
> [<ffffffffc1730c3c>] fuse_readpages+0x28c/0x2f0 [fuse]
> [<ffffffffb296ba58>] __do_page_cache_readahead+0x518/0x6d0
>
> Fix this by unlocking fc->lock before request_end() call. Note,
> that it may look strange to have two same lk parameters in
> pcs_fuse_submit(pfc, req, lk, lk), but the current design
> interprets requests submitted with locked lk as async and
> we keep this logic.
>
> Generally, I feel we need to improve design in a thing
> of queueing requests and locking, but we need more
> inverstigation and thinking here, so let's delay this
> to next VZ update.
>
> https://pmc.acronis.com/browse/VSTOR-16246
>
> Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
> ---
> fs/fuse/kio/pcs/pcs_fuse_kdirect.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> index b286a956a751..61415e029c45 100644
> --- a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> +++ b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> @@ -883,7 +883,7 @@ static int pcs_fuse_prep_rw(struct pcs_fuse_req *r)
> return ret;
> }
>
> -static void pcs_fuse_submit(struct pcs_fuse_cluster *pfc, struct fuse_req
> *req, int async)
> +static void pcs_fuse_submit(struct pcs_fuse_cluster *pfc, struct fuse_req
> *req, bool async, bool lk)
> {
> struct pcs_fuse_req *r = pcs_req_from_fuse(req);
> struct fuse_inode *fi = get_fuse_inode(req->io_inode);
> @@ -963,7 +963,11 @@ static void pcs_fuse_submit(struct pcs_fuse_cluster
> *pfc, struct fuse_req *req,
> error:
> DTRACE("do fuse_request_end req:%p op:%d err:%d\n", &r->req,
> r->req.in.h.opcode, r->req.out.h.error);
>
> + if (lk)
> + spin_unlock(&pfc->fc->lock);
We can't unlock fc->lock inside fuse_request_send_background_locked(),
because it breaks compatibility with fuse_set_nowrite(). We must
ensure that no one pending requests should not be between
fuse_set_nowrite() and fuse_release_nowrite(). But since fc unlock
inside fuse_request_send_background_locked() this promise can be broken.
> request_end(pfc->fc, &r->req);
> + if (lk)
> + spin_lock(&pfc->fc->lock);
> return;
>
> submit:
> @@ -1027,7 +1031,7 @@ static void _pcs_shrink_end(struct fuse_conn *fc,
> struct fuse_req *req)
>
> TRACE("resubmit %p\n", &r->req);
> list_del_init(&ireq->list);
> - pcs_fuse_submit(pfc, &r->req, 1);
> + pcs_fuse_submit(pfc, &r->req, true, false);
> }
> }
>
> @@ -1174,7 +1178,7 @@ static int kpcs_req_send(struct fuse_conn* fc, struct
> fuse_req *req, bool bg, bo
> }
> __clear_bit(FR_PENDING, &req->flags);
>
> - pcs_fuse_submit(pfc, req, lk);
> + pcs_fuse_submit(pfc, req, lk, lk);
> if (!bg)
> wait_event(req->waitq,
> test_bit(FR_FINISHED, &req->flags) && !req->end);
>
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