| Message ID | 20240908000704.414538-1-dlemoal@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: Prevent deadlocks when switching elevators | expand |
On Sun, Sep 08, 2024 at 09:07:04AM +0900, 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(). > > Reported-by: Richard W.M. Jones <rjones@redhat.com> > Reported-by: Jiri Jaburek <jjaburek@redhat.com> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166 > Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") > Cc: stable@vger.kernel.org > Signed-off-by: Damien Le Moal <dlemoal@kernel.org> I tested this (using my "unreliable" test!), and it passed 5,000 iterations, so: Tested-by: Richard W.M. Jones <rjones@redhat.com> Thanks, Rich. > --- > 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
On Sun, 08 Sep 2024 09:07:04 +0900, 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. > > [...] Applied, thanks! [1/1] block: Prevent deadlocks when switching elevators commit: 3c031b721c0ee1d6237719a6a9d7487ef757487b Best regards,
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@redhat.com> > Reported-by: Jiri Jaburek <jjaburek@redhat.com> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166 > Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") > Cc: stable@vger.kernel.org > Signed-off-by: Damien Le Moal <dlemoal@kernel.org> > --- > 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,
On 2024-09-24 12:46, Jiri Slaby wrote: > 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 (etc.) Patch here but it's not in mainline yet: https://lore.kernel.org/linux-block/20240917133231.134806-1-dlemoal@kernel.org/ cheers Holger
On 9/24/24 7:08 AM, Holger Hoffstätte wrote: > On 2024-09-24 12:46, Jiri Slaby wrote: >> 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 > > (etc.) > > Patch here but it's not in mainline yet: > > https://lore.kernel.org/linux-block/20240917133231.134806-1-dlemoal@kernel.org/ It'll go upstream later this week.
On 24. 09. 24, 16:34, Jens Axboe wrote: > On 9/24/24 7:08 AM, Holger Hoffstätte wrote: >> On 2024-09-24 12:46, Jiri Slaby wrote: >>> 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 >> >> (etc.) >> >> Patch here but it's not in mainline yet: >> >> https://lore.kernel.org/linux-block/20240917133231.134806-1-dlemoal@kernel.org/ > > It'll go upstream later this week. FWIW works for me. thanks,
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 *);
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@redhat.com> Reported-by: Jiri Jaburek <jjaburek@redhat.com> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166 Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") Cc: stable@vger.kernel.org Signed-off-by: Damien Le Moal <dlemoal@kernel.org> --- block/blk-sysfs.c | 22 +++++++++++++++++++++- block/elevator.c | 21 +++++++++++++++------ block/elevator.h | 2 ++ 3 files changed, 38 insertions(+), 7 deletions(-)