| Message ID | 20240908000704.414538-1-dlemoal@kernel.org (mailing list archive) |
|---|---|
| State | New |
| 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,
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(-)