On 08. 09. 24, 2:07, Damien Le Moal wrote:
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().
Hi,
this broke udev rules for loop in 6.11:
> loop1: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop1/queue/scheduler}="none", ignoring:
No such file or directory
> loop0: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop0/queue/scheduler}="none", ignoring:
No such file or directory
> loop5: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop5/queue/scheduler}="none", ignoring:
No such file or directory
> loop3: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop3/queue/scheduler}="none", ignoring:
No such file or directory
> loop2: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop2/queue/scheduler}="none", ignoring:
No such file or directory
> loop7: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop7/queue/scheduler}="none", ignoring:
No such file or directory
> loop4: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop4/queue/scheduler}="none", ignoring:
No such file or directory
> loop6: /usr/lib/udev/rules.d/60-io-scheduler.rules:25 Failed to write
ATTR{/sys/devices/virtual/block/loop6/queue/scheduler}="none", ignoring:
No such file or directory
60-io-scheduler.rules:
1 # Set optimal IO schedulers for HDD and SSD
2 # Copyright (c) 2021 SUSE LLC
3
4 # ## DO NOT EDIT. ##
5 # To modify the rules, copy this file to /etc/udev/rules.d/60-io-scheduler.rules
6 # and edit the copy.
7 # Please read the section "Tuning I/O performance" in the System Analysis and Tuning Guide
8 # from the SUSE Documentation.
9
10 # --- DO NOT EDIT THIS PART ----
11 SUBSYSTEM!="block", GOTO="scheduler_end"
12 ACTION!="add|change", GOTO="scheduler_end"
13 ENV{DEVTYPE}!="disk", GOTO="scheduler_end"
14 TEST!="%S%p/queue/scheduler", GOTO="scheduler_end"
It apparently exists here ^^^.
15
16 # For dm devices, the relevant events are "change" events, see 10-dm.rules
17 ACTION!="change", KERNEL=="dm-*", GOTO="scheduler_end"
18 # "none" with no brackets means scheduler isn't configurable
19 ATTR{queue/scheduler}=="none", GOTO="scheduler_end"
20 # keep our hands off zoned devices, the kernel auto-configures them
21 ATTR{queue/zoned}!="none", GOTO="scheduler_end"
22 # Enforce "none" for multipath components.
23 ENV{DM_MULTIPATH_DEVICE_PATH}=="1", ATTR{queue/scheduler}="none", GOTO="scheduler_end"
24 # Enforce "none" for loop devices
25 KERNEL=="loop[0-9]*", ATTR{queue/scheduler}="none", GOTO="scheduler_end"
But cannot be written to ^^^ because it does not exist. What the heck?
26
27 # --- EDIT BELOW HERE after copying to /etc/udev/rules.d ---
28
29 # Uncomment these if you want to force virtual devices to use no scheduler
30 # KERNEL=="vd[a-z]*", ATTR{queue/scheduler}="none", GOTO="scheduler_end"
31 # KERNEL=="xvd[a-z]*", ATTR{queue/scheduler}="none", GOTO="scheduler_end"
32
33 # Leave virtual devices untouched
34 KERNEL=="vd[a-z]*", GOTO="scheduler_end"
35 KERNEL=="xvd[a-z]*", GOTO="scheduler_end"
36
37 # 1. BFQ scheduler for single-queue HDD
38 ATTR{queue/rotational}!="0", TEST!="%S%p/mq/1", ATTR{queue/scheduler}="bfq", GOTO="scheduler_end"
39
40 # 2. BFQ scheduler for every HDD, including "real" multiqueue
41 # ATTR{queue/rotational}!="0", ATTR{queue/scheduler}="bfq", GOTO="scheduler_end"
42
43 # 3. For "real" multiqueue devices, the kernel defaults to no IO scheduling
44 # Uncomment this (and select your scheduler) if you need an IO scheduler for them
45 # TEST=="%S%p/mq/1", ATTR{queue/scheduler}="kyber", GOTO="scheduler_end"
46
47 # 4. BFQ scheduler for every device (uncomment if you need ionice or blk-cgroup features)
48 # ATTR{queue/scheduler}="bfq", GOTO="scheduler_end"
49
50 # 5. mq-deadline is the kernel default for devices with just one hardware queue
51 # ATTR{queue/scheduler}="mq-deadline"
52
53 # --- EDIT ABOVE HERE after copying to /etc/udev/rules.d ---
54 LABEL="scheduler_end"
Any ideas?
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 *);
thanks,
--
js
suse labs
