Hi Joanne, On 7/17/24 23:34, Joanne Koong wrote: > There are situations where fuse servers can become unresponsive or take > too long to reply to a request. Currently there is no upper bound on > how long a request may take, which may be frustrating to users who get > stuck waiting for a request to complete. > > This commit adds a daemon timeout option (in seconds) for fuse requests. > If the timeout elapses before the request is replied to, the request will > fail with -ETIME. > > There are 3 possibilities for a request that times out: > a) The request times out before the request has been sent to userspace > b) The request times out after the request has been sent to userspace > and before it receives a reply from the server > c) The request times out after the request has been sent to userspace > and the server replies while the kernel is timing out the request > > Proper synchronization must be added to ensure that the request is > handled correctly in all of these cases. To this effect, there is a new > FR_PROCESSING bit added to the request flags, which is set atomically by > either the timeout handler (see fuse_request_timeout()) which is invoked > after the request timeout elapses or set by the request reply handler > (see dev_do_write()), whichever gets there first. > > If the reply handler and the timeout handler are executing simultaneously > and the reply handler sets FR_PROCESSING before the timeout handler, then > the request is re-queued onto the waitqueue and the kernel will process the > reply as though the timeout did not elapse. If the timeout handler sets > FR_PROCESSING before the reply handler, then the request will fail with > -ETIME and the request will be cleaned up. > > Proper acquires on the request reference must be added to ensure that the > timeout handler does not drop the last refcount on the request while the > reply handler (dev_do_write()) or forwarder handler (dev_do_read()) is > still accessing the request. (By "forwarder handler", this is the handler > that forwards the request to userspace). > > Currently, this is the lifecycle of the request refcount: > > Request is created: > fuse_simple_request -> allocates request, sets refcount to 1 > __fuse_request_send -> acquires refcount > queues request and waits for reply... > fuse_simple_request -> drops refcount > > Request is freed: > fuse_dev_do_write > fuse_request_end -> drops refcount on request > > The timeout handler drops the refcount on the request so that the > request is properly cleaned up if a reply is never received. Because of > this, both the forwarder handler and the reply handler must acquire a refcount > on the request while it accesses the request, and the refcount must be > acquired while the lock of the list the request is on is held. > > There is a potential race if the request is being forwarded to > userspace while the timeout handler is executing (eg FR_PENDING has > already been cleared but dev_do_read() hasn't finished executing). This > is a problem because this would free the request but the request has not > been removed from the fpq list it's on. To prevent this, dev_do_read() > must check FR_PROCESSING at the end of its logic and remove the request > from the fpq list if the timeout occurred. > > There is also the case where the connection may be aborted or the > device may be released while the timeout handler is running. To protect > against an extra refcount drop on the request, the timeout handler > checks the connected state of the list and lets the abort handler drop the > last reference if the abort is running simultaneously. Similarly, the > timeout handler also needs to check if the req->out.h.error is set to > -ESTALE, which indicates that the device release is cleaning up the > request. In both these cases, the timeout handler will return without > dropping the refcount. > > Please also note that background requests are not applicable for timeouts > since they are asynchronous. This and that thread here actually make me wonder if this is the right approach https://lore.kernel.org/lkml/20240613040147.329220-1-haifeng.xu@xxxxxxxxxx/T/ In th3 thread above a request got interrupted, but fuse-server still does not manage stop it. From my point of view, interrupting a request suggests to add a rather short kernel lifetime for it. With that one either needs to wake up in intervals and check if request timeout got exceeded or it needs to be an async kernel thread. I think that async thread would also allow to give a timeout to background requests. Or we add an async timeout to bg and interupted requests additionally? (I only basically reviewed, can't do carefully right now - on vacation and as I just noticed, on a laptop that gives me electric shocks when I connect it to power.) Thanks, Bernd > > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx> > --- > fs/fuse/dev.c | 177 ++++++++++++++++++++++++++++++++++++++++++++--- > fs/fuse/fuse_i.h | 12 ++++ > fs/fuse/inode.c | 7 ++ > 3 files changed, 188 insertions(+), 8 deletions(-) > > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c > index 9eb191b5c4de..7dd7b244951b 100644 > --- a/fs/fuse/dev.c > +++ b/fs/fuse/dev.c > @@ -331,6 +331,69 @@ void fuse_request_end(struct fuse_req *req) > } > EXPORT_SYMBOL_GPL(fuse_request_end); > > +/* fuse_request_end for requests that timeout */ > +static void fuse_request_timeout(struct fuse_req *req) > +{ > + struct fuse_conn *fc = req->fm->fc; > + struct fuse_iqueue *fiq = &fc->iq; > + struct fuse_pqueue *fpq; > + > + spin_lock(&fiq->lock); > + if (!fiq->connected) { > + spin_unlock(&fiq->lock); > + /* > + * Connection is being aborted. The abort will release > + * the refcount on the request > + */ > + req->out.h.error = -ECONNABORTED; > + return; > + } > + if (test_bit(FR_PENDING, &req->flags)) { > + /* Request is not yet in userspace, bail out */ > + list_del(&req->list); > + spin_unlock(&fiq->lock); > + req->out.h.error = -ETIME; > + __fuse_put_request(req); > + return; > + } > + if (test_bit(FR_INTERRUPTED, &req->flags)) > + list_del_init(&req->intr_entry); > + > + fpq = req->fpq; > + spin_unlock(&fiq->lock); > + > + if (fpq) { > + spin_lock(&fpq->lock); > + if (!fpq->connected && (!test_bit(FR_PRIVATE, &req->flags))) { > + spin_unlock(&fpq->lock); > + /* > + * Connection is being aborted. The abort will release > + * the refcount on the request > + */ > + req->out.h.error = -ECONNABORTED; > + return; > + } > + if (req->out.h.error == -ESTALE) { > + /* > + * Device is being released. The fuse_dev_release call > + * will drop the refcount on the request > + */ > + spin_unlock(&fpq->lock); > + return; > + } > + if (!test_bit(FR_PRIVATE, &req->flags)) > + list_del_init(&req->list); > + spin_unlock(&fpq->lock); > + } > + > + req->out.h.error = -ETIME; > + > + if (test_bit(FR_ASYNC, &req->flags)) > + req->args->end(req->fm, req->args, req->out.h.error); > + > + fuse_put_request(req); > +} > + > static int queue_interrupt(struct fuse_req *req) > { > struct fuse_iqueue *fiq = &req->fm->fc->iq; > @@ -361,6 +424,62 @@ static int queue_interrupt(struct fuse_req *req) > return 0; > } > > +enum wait_type { > + WAIT_TYPE_INTERRUPTIBLE, > + WAIT_TYPE_KILLABLE, > + WAIT_TYPE_NONINTERRUPTIBLE, > +}; > + > +static int fuse_wait_event_interruptible_timeout(struct fuse_req *req) > +{ > + struct fuse_conn *fc = req->fm->fc; > + > + return wait_event_interruptible_timeout(req->waitq, > + test_bit(FR_FINISHED, > + &req->flags), > + fc->daemon_timeout); > +} > +ALLOW_ERROR_INJECTION(fuse_wait_event_interruptible_timeout, ERRNO); > + > +static int wait_answer_timeout(struct fuse_req *req, enum wait_type type) > +{ > + struct fuse_conn *fc = req->fm->fc; > + int err; > + > +wait_answer_start: > + if (type == WAIT_TYPE_INTERRUPTIBLE) > + err = fuse_wait_event_interruptible_timeout(req); > + else if (type == WAIT_TYPE_KILLABLE) > + err = wait_event_killable_timeout(req->waitq, > + test_bit(FR_FINISHED, &req->flags), > + fc->daemon_timeout); > + > + else if (type == WAIT_TYPE_NONINTERRUPTIBLE) > + err = wait_event_timeout(req->waitq, test_bit(FR_FINISHED, &req->flags), > + fc->daemon_timeout); > + else > + WARN_ON(1); > + > + /* request was answered */ > + if (err > 0) > + return 0; > + > + /* request was not answered in time */ > + if (err == 0) { > + if (test_and_set_bit(FR_PROCESSING, &req->flags)) > + /* request reply is being processed by kernel right now. > + * we should wait for the answer. > + */ > + goto wait_answer_start; > + > + fuse_request_timeout(req); > + return 0; > + } > + > + /* else request was interrupted */ > + return err; > +} > + > static void request_wait_answer(struct fuse_req *req) > { > struct fuse_conn *fc = req->fm->fc; > @@ -369,8 +488,11 @@ static void request_wait_answer(struct fuse_req *req) > > if (!fc->no_interrupt) { > /* Any signal may interrupt this */ > - err = wait_event_interruptible(req->waitq, > - test_bit(FR_FINISHED, &req->flags)); > + if (fc->daemon_timeout) > + err = wait_answer_timeout(req, WAIT_TYPE_INTERRUPTIBLE); > + else > + err = wait_event_interruptible(req->waitq, > + test_bit(FR_FINISHED, &req->flags)); > if (!err) > return; > > @@ -383,8 +505,11 @@ static void request_wait_answer(struct fuse_req *req) > > if (!test_bit(FR_FORCE, &req->flags)) { > /* Only fatal signals may interrupt this */ > - err = wait_event_killable(req->waitq, > - test_bit(FR_FINISHED, &req->flags)); > + if (fc->daemon_timeout) > + err = wait_answer_timeout(req, WAIT_TYPE_KILLABLE); > + else > + err = wait_event_killable(req->waitq, > + test_bit(FR_FINISHED, &req->flags)); > if (!err) > return; > > @@ -404,7 +529,10 @@ static void request_wait_answer(struct fuse_req *req) > * Either request is already in userspace, or it was forced. > * Wait it out. > */ > - wait_event(req->waitq, test_bit(FR_FINISHED, &req->flags)); > + if (fc->daemon_timeout) > + wait_answer_timeout(req, WAIT_TYPE_NONINTERRUPTIBLE); > + else > + wait_event(req->waitq, test_bit(FR_FINISHED, &req->flags)); > } > > static void __fuse_request_send(struct fuse_req *req) > @@ -1268,6 +1396,9 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, > req = list_entry(fiq->pending.next, struct fuse_req, list); > clear_bit(FR_PENDING, &req->flags); > list_del_init(&req->list); > + /* Acquire a reference since fuse_request_timeout may also be executing */ > + __fuse_get_request(req); > + req->fpq = fpq; > spin_unlock(&fiq->lock); > > args = req->args; > @@ -1280,6 +1411,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, > if (args->opcode == FUSE_SETXATTR) > req->out.h.error = -E2BIG; > fuse_request_end(req); > + fuse_put_request(req); > goto restart; > } > spin_lock(&fpq->lock); > @@ -1316,13 +1448,23 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, > } > hash = fuse_req_hash(req->in.h.unique); > list_move_tail(&req->list, &fpq->processing[hash]); > - __fuse_get_request(req); > set_bit(FR_SENT, &req->flags); > spin_unlock(&fpq->lock); > /* matches barrier in request_wait_answer() */ > smp_mb__after_atomic(); > if (test_bit(FR_INTERRUPTED, &req->flags)) > queue_interrupt(req); > + > + /* Check if request timed out */ > + if (test_bit(FR_PROCESSING, &req->flags)) { > + spin_lock(&fpq->lock); > + if (!test_bit(FR_PRIVATE, &req->flags)) > + list_del_init(&req->list); > + spin_unlock(&fpq->lock); > + fuse_put_request(req); > + return -ETIME; > + } > + > fuse_put_request(req); > > return reqsize; > @@ -1332,6 +1474,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, > list_del_init(&req->list); > spin_unlock(&fpq->lock); > fuse_request_end(req); > + fuse_put_request(req); > return err; > > err_unlock: > @@ -1951,9 +2094,10 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud, > goto copy_finish; > } > > + __fuse_get_request(req); > + > /* Is it an interrupt reply ID? */ > if (oh.unique & FUSE_INT_REQ_BIT) { > - __fuse_get_request(req); > spin_unlock(&fpq->lock); > > err = 0; > @@ -1969,6 +2113,13 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud, > goto copy_finish; > } > > + if (test_and_set_bit(FR_PROCESSING, &req->flags)) { > + /* request has timed out already */ > + spin_unlock(&fpq->lock); > + fuse_put_request(req); > + goto copy_finish; > + } > + > clear_bit(FR_SENT, &req->flags); > list_move(&req->list, &fpq->io); > req->out.h = oh; > @@ -1995,6 +2146,7 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud, > spin_unlock(&fpq->lock); > > fuse_request_end(req); > + fuse_put_request(req); > out: > return err ? err : nbytes; > > @@ -2260,13 +2412,22 @@ int fuse_dev_release(struct inode *inode, struct file *file) > if (fud) { > struct fuse_conn *fc = fud->fc; > struct fuse_pqueue *fpq = &fud->pq; > + struct fuse_req *req; > LIST_HEAD(to_end); > unsigned int i; > > spin_lock(&fpq->lock); > WARN_ON(!list_empty(&fpq->io)); > - for (i = 0; i < FUSE_PQ_HASH_SIZE; i++) > + for (i = 0; i < FUSE_PQ_HASH_SIZE; i++) { > + /* > + * Set the req error to -ESTALE so that if the timeout > + * handler tries handling it, it knows it's being > + * released > + */ > + list_for_each_entry(req, &fpq->processing[i], list) > + req->out.h.error = -ESTALE; > list_splice_init(&fpq->processing[i], &to_end); > + } > spin_unlock(&fpq->lock); > > end_requests(&to_end); > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index f23919610313..cbabebbcd5bd 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -375,6 +375,9 @@ struct fuse_io_priv { > * FR_FINISHED: request is finished > * FR_PRIVATE: request is on private list > * FR_ASYNC: request is asynchronous > + * FR_PROCESSING: request is being processed. this gets set when either > + * the reply is getting processed or the kernel is processing > + * a request timeout > */ > enum fuse_req_flag { > FR_ISREPLY, > @@ -389,6 +392,7 @@ enum fuse_req_flag { > FR_FINISHED, > FR_PRIVATE, > FR_ASYNC, > + FR_PROCESSING, > }; > > /** > @@ -435,6 +439,9 @@ struct fuse_req { > > /** fuse_mount this request belongs to */ > struct fuse_mount *fm; > + > + /** page queue this request has been added to */ > + struct fuse_pqueue *fpq; > }; > > struct fuse_iqueue; > @@ -574,6 +581,8 @@ struct fuse_fs_context { > enum fuse_dax_mode dax_mode; > unsigned int max_read; > unsigned int blksize; > + /* Daemon timeout (in seconds). 0 = no timeout (infinite wait) */ > + unsigned int daemon_timeout; > const char *subtype; > > /* DAX device, may be NULL */ > @@ -633,6 +642,9 @@ struct fuse_conn { > /** Constrain ->max_pages to this value during feature negotiation */ > unsigned int max_pages_limit; > > + /* Daemon timeout (in jiffies). 0 = no timeout (infinite wait) */ > + unsigned long daemon_timeout; > + > /** Input queue */ > struct fuse_iqueue iq; > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > index 99e44ea7d875..a2d53a8b8e34 100644 > --- a/fs/fuse/inode.c > +++ b/fs/fuse/inode.c > @@ -733,6 +733,7 @@ enum { > OPT_ALLOW_OTHER, > OPT_MAX_READ, > OPT_BLKSIZE, > + OPT_DAEMON_TIMEOUT, > OPT_ERR > }; > > @@ -747,6 +748,7 @@ static const struct fs_parameter_spec fuse_fs_parameters[] = { > fsparam_u32 ("max_read", OPT_MAX_READ), > fsparam_u32 ("blksize", OPT_BLKSIZE), > fsparam_string ("subtype", OPT_SUBTYPE), > + fsparam_u32 ("daemon_timeout", OPT_DAEMON_TIMEOUT), > {} > }; > > @@ -830,6 +832,10 @@ static int fuse_parse_param(struct fs_context *fsc, struct fs_parameter *param) > ctx->blksize = result.uint_32; > break; > > + case OPT_DAEMON_TIMEOUT: > + ctx->daemon_timeout = result.uint_32; > + break; > + > default: > return -EINVAL; > } > @@ -1724,6 +1730,7 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx) > fc->group_id = ctx->group_id; > fc->legacy_opts_show = ctx->legacy_opts_show; > fc->max_read = max_t(unsigned int, 4096, ctx->max_read); > + fc->daemon_timeout = ctx->daemon_timeout * HZ; > fc->destroy = ctx->destroy; > fc->no_control = ctx->no_control; > fc->no_force_umount = ctx->no_force_umount;
