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

Joanne Koong
2025-01-22T21:56:58Z

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);
+ 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