Re: [PATCH v12 2/2] fuse: add default_request_timeout and max_request_timeout sysctls

[Luis Henriques <luis@igalia.com>]

Hi Joanne,

On Wed, Jan 22 2025, Joanne Koong wrote:

> Introduce two new sysctls, "default_request_timeout" and
> "max_request_timeout". These control how long (in seconds) a server can
> take to reply to a request. If the server does not reply by the timeout,
> then the connection will be aborted. The upper bound on these sysctl
> values is 65535.
>
> "default_request_timeout" sets the default timeout if no timeout is
> specified by the fuse server on mount. 0 (default) indicates no default
> timeout should be enforced. If the server did specify a timeout, then
> default_request_timeout will be ignored.
>
> "max_request_timeout" sets the max amount of time the server may take to
> reply to a request. 0 (default) indicates no maximum timeout. If
> max_request_timeout is set and the fuse server attempts to set a
> timeout greater than max_request_timeout, the system will use
> max_request_timeout as the timeout. Similarly, if default_request_timeout
> is greater than max_request_timeout, the system will use
> max_request_timeout as the timeout. If the server does not request a
> timeout and default_request_timeout is set to 0 but max_request_timeout
> is set, then the timeout will be max_request_timeout.
>
> Please note that these timeouts are not 100% precise. The request may
> take roughly an extra FUSE_TIMEOUT_TIMER_FREQ seconds beyond the set max
> timeout due to how it's internally implemented.
>
> $ sysctl -a | grep fuse.default_request_timeout
> fs.fuse.default_request_timeout = 0
>
> $ echo 65536 | sudo tee /proc/sys/fs/fuse/default_request_timeout
> tee: /proc/sys/fs/fuse/default_request_timeout: Invalid argument
>
> $ echo 65535 | sudo tee /proc/sys/fs/fuse/default_request_timeout
> 65535
>
> $ sysctl -a | grep fuse.default_request_timeout
> fs.fuse.default_request_timeout = 65535
>
> $ echo 0 | sudo tee /proc/sys/fs/fuse/default_request_timeout
> 0
>
> $ sysctl -a | grep fuse.default_request_timeout
> fs.fuse.default_request_timeout = 0
>
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> Reviewed-by: Bernd Schubert <bschubert@ddn.com>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
>  Documentation/admin-guide/sysctl/fs.rst | 25 ++++++++++++++++++++++
>  fs/fuse/fuse_i.h                        | 10 +++++++++
>  fs/fuse/inode.c                         | 28 +++++++++++++++++++++++--
>  fs/fuse/sysctl.c                        | 24 +++++++++++++++++++++
>  4 files changed, 85 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/sysctl/fs.rst b/Documentation/admin-guide/sysctl/fs.rst
> index f5ec6c9312e1..35aeb30bed8b 100644
> --- a/Documentation/admin-guide/sysctl/fs.rst
> +++ b/Documentation/admin-guide/sysctl/fs.rst
> @@ -347,3 +347,28 @@ filesystems:
>  ``/proc/sys/fs/fuse/max_pages_limit`` is a read/write file for
>  setting/getting the maximum number of pages that can be used for servicing
>  requests in FUSE.
> +
> +``/proc/sys/fs/fuse/default_request_timeout`` is a read/write file for
> +setting/getting the default timeout (in seconds) for a fuse server to
> +reply to a kernel-issued request in the event where the server did not
> +specify a timeout at mount. If the server set a timeout,
> +then default_request_timeout will be ignored.  The default
> +"default_request_timeout" is set to 0. 0 indicates no default timeout.
> +The maximum value that can be set is 65535.
> +
> +``/proc/sys/fs/fuse/max_request_timeout`` is a read/write file for
> +setting/getting the maximum timeout (in seconds) for a fuse server to
> +reply to a kernel-issued request. A value greater than 0 automatically opts
> +the server into a timeout that will be set to at most "max_request_timeout",
> +even if the server did not specify a timeout and default_request_timeout is
> +set to 0. If max_request_timeout is greater than 0 and the server set a timeout
> +greater than max_request_timeout or default_request_timeout is set to a value
> +greater than max_request_timeout, the system will use max_request_timeout as the
> +timeout. 0 indicates no max request timeout. The maximum value that can be set
> +is 65535.
> +
> +For timeouts, if the server does not respond to the request by the time
> +the set timeout elapses, then the connection to the fuse server will be aborted.
> +Please note that the timeouts are not 100% precise (eg you may set 60 seconds but
> +the timeout may kick in after 70 seconds). The upper margin of error for the
> +timeout is roughly FUSE_TIMEOUT_TIMER_FREQ seconds.
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 1321cc4ed2ab..e5114831798f 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -49,6 +49,16 @@ extern const unsigned long fuse_timeout_timer_freq;
>  
>  /** Maximum of max_pages received in init_out */
>  extern unsigned int fuse_max_pages_limit;
> +/*
> + * Default timeout (in seconds) for the server to reply to a request
> + * before the connection is aborted, if no timeout was specified on mount.
> + */
> +extern unsigned int fuse_default_req_timeout;
> +/*
> + * Max timeout (in seconds) for the server to reply to a request before
> + * the connection is aborted.
> + */
> +extern unsigned int fuse_max_req_timeout;
>  
>  /** List of active connections */
>  extern struct list_head fuse_conn_list;
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 79ebeb60015c..4e36d99fae52 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -37,6 +37,9 @@ DEFINE_MUTEX(fuse_mutex);
>  static int set_global_limit(const char *val, const struct kernel_param *kp);
>  
>  unsigned int fuse_max_pages_limit = 256;
> +/* default is no timeout */
> +unsigned int fuse_default_req_timeout = 0;
> +unsigned int fuse_max_req_timeout = 0;
>  
>  unsigned max_user_bgreq;
>  module_param_call(max_user_bgreq, set_global_limit, param_get_uint,
> @@ -1268,6 +1271,24 @@ static void set_request_timeout(struct fuse_conn *fc, unsigned int timeout)
>  			   fuse_timeout_timer_freq);
>  }
>  
> +static void init_server_timeout(struct fuse_conn *fc, unsigned int timeout)
> +{
> +	if (!timeout && !fuse_max_req_timeout && !fuse_default_req_timeout)
> +		return;
> +
> +	if (!timeout)
> +		timeout = fuse_default_req_timeout;
> +
> +	if (fuse_max_req_timeout) {
> +		if (timeout)
> +			timeout = min(fuse_max_req_timeout, timeout);

Sorry for this late comment (this is v12 already!), but I wonder if it
would be worth to use clamp() instead of min().  Limiting this value to
the range [FUSE_TIMEOUT_TIMER_FREQ, fuxe_max_req_timeout] would prevent
accidentally setting the timeout to a very low value.

There are also some white-spaces/tabs issues with the other patch, which
are worth fixing before merging.  Other than that, feel free to add my

Reviewed-by: Luis Henriques <luis@igalia.com>

Cheers,
-- 
Luís

> +		else
> +			timeout = fuse_max_req_timeout;
> +	}
> +
> +	set_request_timeout(fc, timeout);
> +}
> +
>  struct fuse_init_args {
>  	struct fuse_args args;
>  	struct fuse_init_in in;
> @@ -1286,6 +1307,7 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
>  		ok = false;
>  	else {
>  		unsigned long ra_pages;
> +		unsigned int timeout = 0;
>  
>  		process_init_limits(fc, arg);
>  
> @@ -1404,14 +1426,16 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
>  			if (flags & FUSE_OVER_IO_URING && fuse_uring_enabled())
>  				fc->io_uring = 1;
>  
> -			if ((flags & FUSE_REQUEST_TIMEOUT) && arg->request_timeout)
> -				set_request_timeout(fc, arg->request_timeout);
> +			if (flags & FUSE_REQUEST_TIMEOUT)
> +				timeout = arg->request_timeout;
>  		} else {
>  			ra_pages = fc->max_read / PAGE_SIZE;
>  			fc->no_lock = 1;
>  			fc->no_flock = 1;
>  		}
>  
> +		init_server_timeout(fc, timeout);
> +
>  		fm->sb->s_bdi->ra_pages =
>  				min(fm->sb->s_bdi->ra_pages, ra_pages);
>  		fc->minor = arg->minor;
> diff --git a/fs/fuse/sysctl.c b/fs/fuse/sysctl.c
> index b272bb333005..3d542ef9d889 100644
> --- a/fs/fuse/sysctl.c
> +++ b/fs/fuse/sysctl.c
> @@ -13,6 +13,12 @@ static struct ctl_table_header *fuse_table_header;
>  /* Bound by fuse_init_out max_pages, which is a u16 */
>  static unsigned int sysctl_fuse_max_pages_limit = 65535;
>  
> +/*
> + * fuse_init_out request timeouts are u16.
> + * This goes up to ~18 hours, which is plenty for a timeout.
> + */
> +static unsigned int sysctl_fuse_req_timeout_limit = 65535;
> +
>  static struct ctl_table fuse_sysctl_table[] = {
>  	{
>  		.procname	= "max_pages_limit",
> @@ -23,6 +29,24 @@ static struct ctl_table fuse_sysctl_table[] = {
>  		.extra1		= SYSCTL_ONE,
>  		.extra2		= &sysctl_fuse_max_pages_limit,
>  	},
> +	{
> +		.procname	= "default_request_timeout",
> +		.data		= &fuse_default_req_timeout,
> +		.maxlen		= sizeof(fuse_default_req_timeout),
> +		.mode		= 0644,
> +		.proc_handler	= proc_douintvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= &sysctl_fuse_req_timeout_limit,
> +	},
> +	{
> +		.procname	= "max_request_timeout",
> +		.data		= &fuse_max_req_timeout,
> +		.maxlen		= sizeof(fuse_max_req_timeout),
> +		.mode		= 0644,
> +		.proc_handler	= proc_douintvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= &sysctl_fuse_req_timeout_limit,
> +	},
>  };
>  
>  int fuse_sysctl_register(void)
> -- 
> 2.43.5
>