fuse: add default_request_timeout and max_request_timeout sysctls

joannekoong · Miklos Szeredi · commit 9b17cb59a7db · 2025-03-31T14:59:27.000+02:00
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

[Luis Henriques: Limit the timeout to the range [FUSE_TIMEOUT_TIMER_FREQ,
fuse_max_req_timeout]]

Signed-off-by: Joanne Koong &lt;joannelkoong@gmail.com&gt;
Reviewed-by: Bernd Schubert &lt;bschubert@ddn.com&gt;
Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Reviewed-by: Sergey Senozhatsky &lt;senozhatsky@chromium.org&gt;
Reviewed-by: Luis Henriques &lt;luis@igalia.com&gt;
Reviewed-by: Jeff Layton &lt;jlayton@kernel.org&gt;
Signed-off-by: Miklos Szeredi &lt;mszeredi@redhat.com&gt;
diff --git 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/dev.c b/fs/fuse/dev.c
@@ -32,9 +32,6 @@ MODULE_ALIAS("devname:fuse");
 
 static struct kmem_cache *fuse_req_cachep;
 
-/* Frequency (in seconds) of request timeout checks, if opted into */
-#define FUSE_TIMEOUT_TIMER_FREQ 15
-
 const unsigned long fuse_timeout_timer_freq =
 	secs_to_jiffies(FUSE_TIMEOUT_TIMER_FREQ);
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
@@ -44,11 +44,24 @@
 /** Number of dentries for each connection in the control filesystem */
 #define FUSE_CTL_NUM_DENTRIES 5
 
+/* Frequency (in seconds) of request timeout checks, if opted into */
+#define FUSE_TIMEOUT_TIMER_FREQ 15
+
 /** Frequency (in jiffies) of request timeout checks, if opted into */
 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
@@ -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;
+unsigned int fuse_max_req_timeout;
 
 unsigned max_user_bgreq;
 module_param_call(max_user_bgreq, set_global_limit, param_get_uint,
@@ -1268,6 +1271,26 @@ 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);
+		else
+			timeout = fuse_max_req_timeout;
+	}
+
+	timeout = max(FUSE_TIMEOUT_TIMER_FREQ, timeout);
+
+	set_request_timeout(fc, timeout);
+}
+
 struct fuse_init_args {
 	struct fuse_args args;
 	struct fuse_init_in in;
@@ -1286,6 +1309,7 @@ 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 +1428,16 @@ 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
@@ -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 const struct ctl_table fuse_sysctl_table[] = {
 	{
 		.procname	= "max_pages_limit",
@@ -23,6 +29,24 @@ static const 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)
