On Mon, 2025-02-03 at 09:31 -0800, Joanne Koong wrote:
> On Mon, Feb 3, 2025 at 8:37 AM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> >
> > Add a new file to the "connections" directory that shows how long (in
> > seconds) the oldest fuse_req in the processing hash or pending queue has
> > been waiting.
> >
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > This is based on top of Joanne's work, as it requires the "create_time"
> > field in fuse_req. We have some internal detection of hung fuse server
> > processes that relies on seeing elevated values in the "waiting" sysfs
> > file. The problem with that method is that it can't detect when highly
> > serialized workloads on a FUSE mount are hung. This adds another metric
> > that we can use to detect when fuse mounts are hung.
> > ---
> > fs/fuse/control.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > fs/fuse/fuse_i.h | 2 +-
> > 2 files changed, 57 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/fuse/control.c b/fs/fuse/control.c
> > index 2a730d88cc3bdb50ea1f8a3185faad5f05fc6e74..b213db11a2d7d85c4403baa61f9f7850fed150a8 100644
> > --- a/fs/fuse/control.c
> > +++ b/fs/fuse/control.c
> > @@ -180,6 +180,55 @@ static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
> > return ret;
> > }
> >
> > +/* Show how long (in s) the oldest request has been waiting */
> > +static ssize_t fuse_conn_oldest_read(struct file *file, char __user *buf,
> > + size_t len, loff_t *ppos)
> > +{
> > + char tmp[32];
> > + size_t size;
> > + unsigned long oldest = jiffies;
> > +
> > + if (!*ppos) {
> > + struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
> > + struct fuse_iqueue *fiq = &fc->iq;
> > + struct fuse_dev *fud;
> > + struct fuse_req *req;
> > +
> > + if (!fc)
> > + return 0;
> > +
> > + spin_lock(&fc->lock);
> > + list_for_each_entry(fud, &fc->devices, entry) {
> > + struct fuse_pqueue *fpq = &fud->pq;
> > + int i;
> > +
> > + spin_lock(&fpq->lock);
> > + for (i = 0; i < FUSE_PQ_HASH_SIZE; i++) {
> > + if (list_empty(&fpq->processing[i]))
> > + continue;
> > + /*
> > + * Only check the first request in the queue. The
> > + * assumption is that the one at the head of the list
> > + * will always be the oldest.
> > + */
> > + req = list_first_entry(&fpq->processing[i], struct fuse_req, list);
>
> This probably doesn't matter in actuality, but maybe
> list_first_entry_or_null() on fpq->processing[i] would be more optimal
> here than "list_empty()" and "list_first_entry()" since that'll
> minimize the number of READ_ONCE() calls we'd need to do.
>
I don't think the above will do more than one READ_ONCE, but I agree
that list_first_entry_or_null() is more idiomatic. I'll switch to that.
> > + if (req->create_time < oldest)
> > + oldest = req->create_time;
> > + }
> > + spin_unlock(&fpq->lock);
> > + }
> > + if (!list_empty(&fiq->pending)) {
>
> I think we'll need to grab the fiq->lock here first before checking fiq->pending
>
Doh! Will fix.
> > + req = list_first_entry(&fiq->pending, struct fuse_req, list);
> > + if (req->create_time < oldest)
> > + oldest = req->create_time;
> > + }
> > + spin_unlock(&fc->lock);
> > + fuse_conn_put(fc);
> > + }
> > + size = sprintf(tmp, "%ld\n", (jiffies - oldest)/HZ);
>
> If there are no requests, I think this will still return a non-zero
> value since jiffies is a bit more than what the last "oldest =
> jiffies" was, which might be confusing. Maybe we should just return 0
> in this case?
>
>
You should only see a non-zero value in that case if it takes more than
a second to walk the hash. Possible, but pretty unlikely.
> > + return simple_read_from_buffer(buf, len, ppos, tmp, size);
> > +}
> > +
> > static const struct file_operations fuse_ctl_abort_ops = {
> > .open = nonseekable_open,
> > .write = fuse_conn_abort_write,
> > @@ -202,6 +251,11 @@ static const struct file_operations fuse_conn_congestion_threshold_ops = {
> > .write = fuse_conn_congestion_threshold_write,
> > };
> >
> > +static const struct file_operations fuse_ctl_oldest_ops = {
> > + .open = nonseekable_open,
> > + .read = fuse_conn_oldest_read,
> > +};
> > +
> > static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
> > struct fuse_conn *fc,
> > const char *name,
> > @@ -264,6 +318,8 @@ int fuse_ctl_add_conn(struct fuse_conn *fc)
> >
> > if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400, 1,
> > NULL, &fuse_ctl_waiting_ops) ||
> > + !fuse_ctl_add_dentry(parent, fc, "oldest", S_IFREG | 0400, 1,
> > + NULL, &fuse_ctl_oldest_ops) ||
> > !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200, 1,
> > NULL, &fuse_ctl_abort_ops) ||
> > !fuse_ctl_add_dentry(parent, fc, "max_background", S_IFREG | 0600,
> > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> > index dcc1c327a0574b1fd1adda4b7ca047aa353b6a0a..b46c26bc977ad2d75d10fb306d3ecc4caf2c53bd 100644
> > --- a/fs/fuse/fuse_i.h
> > +++ b/fs/fuse/fuse_i.h
> > @@ -42,7 +42,7 @@
> > #define FUSE_NAME_MAX 1024
> >
> > /** Number of dentries for each connection in the control filesystem */
> > -#define FUSE_CTL_NUM_DENTRIES 5
> > +#define FUSE_CTL_NUM_DENTRIES 6
> >
> > /* Frequency (in seconds) of request timeout checks, if opted into */
> > #define FUSE_TIMEOUT_TIMER_FREQ 15
> >
> > ---
> > base-commit: 9afd7336f3acbe5678cca3b3bc5baefb51ce9564
> > change-id: 20250203-fuse-sysfs-ce351d105cf0
> >
> > Best regards,
> > --
> > Jeff Layton <jlayton@xxxxxxxxxx>
> >
> >
Thanks for the review!
--
Jeff Layton <jlayton@xxxxxxxxxx>
