[PATCH v10 2/2] fuse: add default_request_timeout and max_request_timeout sysctls

[Joanne Koong <joannelkoong@gmail.com>]

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 U32_MAX.

"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 4294967296 | sudo tee /proc/sys/fs/fuse/default_request_timeout
tee: /proc/sys/fs/fuse/default_request_timeout: Invalid argument

$ echo 4294967295 | sudo tee /proc/sys/fs/fuse/default_request_timeout
4294967295

$ sysctl -a | grep fuse.default_request_timeout
fs.fuse.default_request_timeout = 4294967295

$ 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>
---
 Documentation/admin-guide/sysctl/fs.rst | 25 +++++++++++++++++++++++++
 fs/fuse/fuse_i.h                        | 10 ++++++++++
 fs/fuse/inode.c                         | 16 ++++++++++++++--
 fs/fuse/sysctl.c                        | 14 ++++++++++++++
 4 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/fs.rst b/Documentation/admin-guide/sysctl/fs.rst
index f5ec6c9312e1..12169a5e19dd 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 U32_MAX.
+
+``/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 U32_MAX.
+
+For the 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 26eb00e5f043..310885b51087 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -46,6 +46,16 @@
 
 /** 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 02dac88d922e..9f0be79eab74 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -36,6 +36,9 @@ 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,
@@ -1733,8 +1736,17 @@ EXPORT_SYMBOL_GPL(fuse_init_fs_context_submount);
 
 static void fuse_init_fc_timeout(struct fuse_conn *fc, struct fuse_fs_context *ctx)
 {
-	if (ctx->req_timeout) {
-		if (check_mul_overflow(ctx->req_timeout, HZ, &fc->timeout.req_timeout))
+	unsigned int timeout = ctx->req_timeout ?: fuse_default_req_timeout;
+
+	if (fuse_max_req_timeout) {
+		if (!timeout)
+			timeout = fuse_max_req_timeout;
+		else
+			timeout = min(timeout, fuse_max_req_timeout);
+	}
+
+	if (timeout) {
+		if (check_mul_overflow(timeout, HZ, &fc->timeout.req_timeout))
 			fc->timeout.req_timeout = ULONG_MAX;
 
 		INIT_DELAYED_WORK(&fc->timeout.work, fuse_check_timeout);
diff --git a/fs/fuse/sysctl.c b/fs/fuse/sysctl.c
index b272bb333005..5017059513f1 100644
--- a/fs/fuse/sysctl.c
+++ b/fs/fuse/sysctl.c
@@ -23,6 +23,20 @@ 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,
+	},
+	{
+		.procname	= "max_request_timeout",
+		.data		= &fuse_max_req_timeout,
+		.maxlen		= sizeof(fuse_max_req_timeout),
+		.mode		= 0644,
+		.proc_handler	= proc_douintvec,
+	},
 };
 
 int fuse_sysctl_register(void)
-- 
2.43.5