Commit af2814149883 ("block: freeze the queue in queue_attr_store")
changed queue_attr_store() to always freeze a sysfs attribute queue
before calling the attribute store() method, to ensure that no IOs are
in-flight when an attribute value is being updated.
However, this change created a potential deadlock situation for the
scheduler queue attribute as changing the queue elevator with
elv_iosched_store() can result in a call to request_module() if the user
requested module is not already registered. If the file of the requested
module is stored on the block device of the frozen queue, a deadlock
will happen as the read operations triggered by request_module() will
wait for the queue freeze to end.
Solve this issue by introducing the load_module method in struct
queue_sysfs_entry, and to calling this method function in
queue_attr_store() before freezing the attribute queue.
The macro definition QUEUE_RW_LOAD_MODULE_ENTRY() is added to define a
queue sysfs attribute that needs loading a module.
The definition of the scheduler atrribute is changed to using
QUEUE_RW_LOAD_MODULE_ENTRY(), with the function
elv_iosched_load_module() defined as the load_module method.
elv_iosched_store() can then be simplified to remove the call to
request_module().
Reported-by: Richard W.M. Jones <rjones@xxxxxxxxxx>
Reported-by: Jiri Jaburek <jjaburek@xxxxxxxxxx>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166
Fixes: af2814149883 ("block: freeze the queue in queue_attr_store")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
---
block/blk-sysfs.c | 22 +++++++++++++++++++++-
block/elevator.c | 21 +++++++++++++++------
block/elevator.h | 2 ++
3 files changed, 38 insertions(+), 7 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 60116d13cb80..e85941bec857 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -23,6 +23,7 @@
struct queue_sysfs_entry {
struct attribute attr;
ssize_t (*show)(struct gendisk *disk, char *page);
+ int (*load_module)(struct gendisk *disk, const char *page, size_t count);
ssize_t (*store)(struct gendisk *disk, const char *page, size_t count);
};
@@ -413,6 +414,14 @@ static struct queue_sysfs_entry _prefix##_entry = { \
.store = _prefix##_store, \
};
+#define QUEUE_RW_LOAD_MODULE_ENTRY(_prefix, _name) \
+static struct queue_sysfs_entry _prefix##_entry = { \
+ .attr = { .name = _name, .mode = 0644 }, \
+ .show = _prefix##_show, \
+ .load_module = _prefix##_load_module, \
+ .store = _prefix##_store, \
+}
+
QUEUE_RW_ENTRY(queue_requests, "nr_requests");
QUEUE_RW_ENTRY(queue_ra, "read_ahead_kb");
QUEUE_RW_ENTRY(queue_max_sectors, "max_sectors_kb");
@@ -420,7 +429,7 @@ QUEUE_RO_ENTRY(queue_max_hw_sectors, "max_hw_sectors_kb");
QUEUE_RO_ENTRY(queue_max_segments, "max_segments");
QUEUE_RO_ENTRY(queue_max_integrity_segments, "max_integrity_segments");
QUEUE_RO_ENTRY(queue_max_segment_size, "max_segment_size");
-QUEUE_RW_ENTRY(elv_iosched, "scheduler");
+QUEUE_RW_LOAD_MODULE_ENTRY(elv_iosched, "scheduler");
QUEUE_RO_ENTRY(queue_logical_block_size, "logical_block_size");
QUEUE_RO_ENTRY(queue_physical_block_size, "physical_block_size");
@@ -670,6 +679,17 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr,
if (!entry->store)
return -EIO;
+ /*
+ * If the attribute needs to load a module, do it before freezing the
+ * queue to ensure that the module file can be read when the request
+ * queue is the one for the device storing the module file.
+ */
+ if (entry->load_module) {
+ res = entry->load_module(disk, page, length);
+ if (res)
+ return res;
+ }
+
blk_mq_freeze_queue(q);
mutex_lock(&q->sysfs_lock);
res = entry->store(disk, page, length);
diff --git a/block/elevator.c b/block/elevator.c
index f13d552a32c8..c355b55d0107 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -698,17 +698,26 @@ static int elevator_change(struct request_queue *q, const char *elevator_name)
return 0;
e = elevator_find_get(q, elevator_name);
- if (!e) {
- request_module("%s-iosched", elevator_name);
- e = elevator_find_get(q, elevator_name);
- if (!e)
- return -EINVAL;
- }
+ if (!e)
+ return -EINVAL;
ret = elevator_switch(q, e);
elevator_put(e);
return ret;
}
+int elv_iosched_load_module(struct gendisk *disk, const char *buf,
+ size_t count)
+{
+ char elevator_name[ELV_NAME_MAX];
+
+ if (!elv_support_iosched(disk->queue))
+ return -EOPNOTSUPP;
+
+ strscpy(elevator_name, buf, sizeof(elevator_name));
+
+ return request_module("%s-iosched", strstrip(elevator_name));
+}
+
ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
size_t count)
{
diff --git a/block/elevator.h b/block/elevator.h
index 3fe18e1a8692..2a78544bf201 100644
--- a/block/elevator.h
+++ b/block/elevator.h
@@ -148,6 +148,8 @@ extern void elv_unregister(struct elevator_type *);
* io scheduler sysfs switching
*/
ssize_t elv_iosched_show(struct gendisk *disk, char *page);
+int elv_iosched_load_module(struct gendisk *disk, const char *page,
+ size_t count);
ssize_t elv_iosched_store(struct gendisk *disk, const char *page, size_t count);
extern bool elv_bio_merge_ok(struct request *, struct bio *);
--
2.46.0
