Re: [PATCH 4/8] block: add a store_limit operations for sysfs entries

Nilay Shroff
2025-01-07T08:00:42Z

On 1/7/25 12:55 PM, Ming Lei wrote:
> On Tue, Jan 07, 2025 at 07:30:36AM +0100, Christoph Hellwig wrote:
>> De-duplicate the code for updating queue limits by adding a store_limit
>> method that allows having common code handle the actual queue limits
>> update.
>>
>> Note that this is a pure refactoring patch and does not address the
>> existing freeze vs limits lock order problem in the refactored code,
>> which will be addressed next.
>>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> ---
>> block/blk-sysfs.c | 128 ++++++++++++++++++++++------------------------
>> 1 file changed, 61 insertions(+), 67 deletions(-)
>>
>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>> index 767598e719ab..8d69315e986d 100644
>> --- a/block/blk-sysfs.c
>> +++ b/block/blk-sysfs.c
>> @@ -24,6 +24,8 @@ struct queue_sysfs_entry {
>> struct attribute attr;
>> ssize_t (*show)(struct gendisk *disk, char *page);
>> ssize_t (*store)(struct gendisk *disk, const char *page, size_t count);
>> + int (*store_limit)(struct gendisk *disk, const char *page,
>> + size_t count, struct queue_limits *lim);
>> void (*load_module)(struct gendisk *disk, const char *page, size_t count);
>> };
>>
>> @@ -153,13 +155,11 @@ QUEUE_SYSFS_SHOW_CONST(discard_zeroes_data, 0)
>> QUEUE_SYSFS_SHOW_CONST(write_same_max, 0)
>> QUEUE_SYSFS_SHOW_CONST(poll_delay, -1)
>>
>> -static ssize_t queue_max_discard_sectors_store(struct gendisk *disk,
>> - const char *page, size_t count)
>> +static int queue_max_discard_sectors_store(struct gendisk *disk,
>> + const char *page, size_t count, struct queue_limits *lim)
>> {
>> unsigned long max_discard_bytes;
>> - struct queue_limits lim;
>> ssize_t ret;
>> - int err;
>>
>> ret = queue_var_store(&max_discard_bytes, page, count);
>> if (ret < 0)
>> @@ -171,38 +171,28 @@ static ssize_t queue_max_discard_sectors_store(struct gendisk *disk,
>> if ((max_discard_bytes >> SECTOR_SHIFT) > UINT_MAX)
>> return -EINVAL;
>>
>> - lim = queue_limits_start_update(disk->queue);
>> - lim.max_user_discard_sectors = max_discard_bytes >> SECTOR_SHIFT;
>> - err = queue_limits_commit_update(disk->queue, &lim);
>> - if (err)
>> - return err;
>> - return ret;
>> + lim->max_user_discard_sectors = max_discard_bytes >> SECTOR_SHIFT;
>> + return 0;
>> }
>>
>> -static ssize_t
>> -queue_max_sectors_store(struct gendisk *disk, const char *page, size_t count)
>> +static int
>> +queue_max_sectors_store(struct gendisk *disk, const char *page, size_t count,
>> + struct queue_limits *lim)
>> {
>> unsigned long max_sectors_kb;
>> - struct queue_limits lim;
>> ssize_t ret;
>> - int err;
>>
>> ret = queue_var_store(&max_sectors_kb, page, count);
>> if (ret < 0)
>> return ret;
>>
>> - lim = queue_limits_start_update(disk->queue);
>> - lim.max_user_sectors = max_sectors_kb << 1;
>> - err = queue_limits_commit_update(disk->queue, &lim);
>> - if (err)
>> - return err;
>> - return ret;
>> + lim->max_user_sectors = max_sectors_kb << 1;
>> + return 0;
>> }
>>
>> static ssize_t queue_feature_store(struct gendisk *disk, const char *page,
>> - size_t count, blk_features_t feature)
>> + size_t count, struct queue_limits *lim, blk_features_t feature)
>> {
>> - struct queue_limits lim;
>> unsigned long val;
>> ssize_t ret;
>>
>> @@ -210,15 +200,11 @@ static ssize_t queue_feature_store(struct gendisk *disk, const char *page,
>> if (ret < 0)
>> return ret;
>>
>> - lim = queue_limits_start_update(disk->queue);
>> if (val)
>> - lim.features |= feature;
>> + lim->features |= feature;
>> else
>> - lim.features &= ~feature;
>> - ret = queue_limits_commit_update(disk->queue, &lim);
>> - if (ret)
>> - return ret;
>> - return count;
>> + lim->features &= ~feature;
>> + return 0;
>> }
>>
>> #define QUEUE_SYSFS_FEATURE(_name, _feature) \
>> @@ -227,10 +213,10 @@ static ssize_t queue_##_name##_show(struct gendisk *disk, char *page) \
>> return sysfs_emit(page, "%u\n", \
>> !!(disk->queue->limits.features & _feature)); \
>> } \
>> -static ssize_t queue_##_name##_store(struct gendisk *disk, \
>> - const char *page, size_t count) \
>> +static int queue_##_name##_store(struct gendisk *disk, \
>> + const char *page, size_t count, struct queue_limits *lim) \
>> { \
>> - return queue_feature_store(disk, page, count, _feature); \
>> + return queue_feature_store(disk, page, count, lim, _feature); \
>> }
>>
>> QUEUE_SYSFS_FEATURE(rotational, BLK_FEAT_ROTATIONAL)
>> @@ -266,10 +252,9 @@ static ssize_t queue_iostats_passthrough_show(struct gendisk *disk, char *page)
>> return queue_var_show(!!blk_queue_passthrough_stat(disk->queue), page);
>> }
>>
>> -static ssize_t queue_iostats_passthrough_store(struct gendisk *disk,
>> - const char *page, size_t count)
>> +static int queue_iostats_passthrough_store(struct gendisk *disk,
>> + const char *page, size_t count, struct queue_limits *lim)
>> {
>> - struct queue_limits lim;
>> unsigned long ios;
>> ssize_t ret;
>>
>> @@ -277,18 +262,13 @@ static ssize_t queue_iostats_passthrough_store(struct gendisk *disk,
>> if (ret < 0)
>> return ret;
>>
>> - lim = queue_limits_start_update(disk->queue);
>> if (ios)
>> - lim.flags |= BLK_FLAG_IOSTATS_PASSTHROUGH;
>> + lim->flags |= BLK_FLAG_IOSTATS_PASSTHROUGH;
>> else
>> - lim.flags &= ~BLK_FLAG_IOSTATS_PASSTHROUGH;
>> -
>> - ret = queue_limits_commit_update(disk->queue, &lim);
>> - if (ret)
>> - return ret;
>> -
>> - return count;
>> + lim->flags &= ~BLK_FLAG_IOSTATS_PASSTHROUGH;
>> + return 0;
>> }
>> +
>> static ssize_t queue_nomerges_show(struct gendisk *disk, char *page)
>> {
>> return queue_var_show((blk_queue_nomerges(disk->queue) << 1) |
>> @@ -391,12 +371,10 @@ static ssize_t queue_wc_show(struct gendisk *disk, char *page)
>> return sysfs_emit(page, "write through\n");
>> }
>>
>> -static ssize_t queue_wc_store(struct gendisk *disk, const char *page,
>> - size_t count)
>> +static int queue_wc_store(struct gendisk *disk, const char *page,
>> + size_t count, struct queue_limits *lim)
>> {
>> - struct queue_limits lim;
>> bool disable;
>> - int err;
>>
>> if (!strncmp(page, "write back", 10)) {
>> disable = false;
>> @@ -407,15 +385,11 @@ static ssize_t queue_wc_store(struct gendisk *disk, const char *page,
>> return -EINVAL;
>> }
>>
>> - lim = queue_limits_start_update(disk->queue);
>> if (disable)
>> - lim.flags |= BLK_FLAG_WRITE_CACHE_DISABLED;
>> + lim->flags |= BLK_FLAG_WRITE_CACHE_DISABLED;
>> else
>> - lim.flags &= ~BLK_FLAG_WRITE_CACHE_DISABLED;
>> - err = queue_limits_commit_update(disk->queue, &lim);
>> - if (err)
>> - return err;
>> - return count;
>> + lim->flags &= ~BLK_FLAG_WRITE_CACHE_DISABLED;
>> + return 0;
>> }
>>
>> #define QUEUE_RO_ENTRY(_prefix, _name) \
>> @@ -431,6 +405,13 @@ static struct queue_sysfs_entry _prefix##_entry = { \
>> .store = _prefix##_store, \
>> };
>>
>> +#define QUEUE_LIM_RW_ENTRY(_prefix, _name) \
>> +static struct queue_sysfs_entry _prefix##_entry = { \
>> + .attr = { .name = _name, .mode = 0644 }, \
>> + .show = _prefix##_show, \
>> + .store_limit = _prefix##_store, \
>> +}
>> +
>> #define QUEUE_RW_LOAD_MODULE_ENTRY(_prefix, _name) \
>> static struct queue_sysfs_entry _prefix##_entry = { \
>> .attr = { .name = _name, .mode = 0644 }, \
>> @@ -441,7 +422,7 @@ static struct queue_sysfs_entry _prefix##_entry = { \
>>
>> QUEUE_RW_ENTRY(queue_requests, "nr_requests");
>> QUEUE_RW_ENTRY(queue_ra, "read_ahead_kb");
>> -QUEUE_RW_ENTRY(queue_max_sectors, "max_sectors_kb");
>> +QUEUE_LIM_RW_ENTRY(queue_max_sectors, "max_sectors_kb");
>> 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");
>> @@ -457,7 +438,7 @@ QUEUE_RO_ENTRY(queue_io_opt, "optimal_io_size");
>> QUEUE_RO_ENTRY(queue_max_discard_segments, "max_discard_segments");
>> QUEUE_RO_ENTRY(queue_discard_granularity, "discard_granularity");
>> QUEUE_RO_ENTRY(queue_max_hw_discard_sectors, "discard_max_hw_bytes");
>> -QUEUE_RW_ENTRY(queue_max_discard_sectors, "discard_max_bytes");
>> +QUEUE_LIM_RW_ENTRY(queue_max_discard_sectors, "discard_max_bytes");
>> QUEUE_RO_ENTRY(queue_discard_zeroes_data, "discard_zeroes_data");
>>
>> QUEUE_RO_ENTRY(queue_atomic_write_max_sectors, "atomic_write_max_bytes");
>> @@ -477,11 +458,11 @@ QUEUE_RO_ENTRY(queue_max_open_zones, "max_open_zones");
>> QUEUE_RO_ENTRY(queue_max_active_zones, "max_active_zones");
>>
>> QUEUE_RW_ENTRY(queue_nomerges, "nomerges");
>> -QUEUE_RW_ENTRY(queue_iostats_passthrough, "iostats_passthrough");
>> +QUEUE_LIM_RW_ENTRY(queue_iostats_passthrough, "iostats_passthrough");
>> QUEUE_RW_ENTRY(queue_rq_affinity, "rq_affinity");
>> QUEUE_RW_ENTRY(queue_poll, "io_poll");
>> QUEUE_RW_ENTRY(queue_poll_delay, "io_poll_delay");
>> -QUEUE_RW_ENTRY(queue_wc, "write_cache");
>> +QUEUE_LIM_RW_ENTRY(queue_wc, "write_cache");
>> QUEUE_RO_ENTRY(queue_fua, "fua");
>> QUEUE_RO_ENTRY(queue_dax, "dax");
>> QUEUE_RW_ENTRY(queue_io_timeout, "io_timeout");
>> @@ -494,10 +475,10 @@ static struct queue_sysfs_entry queue_hw_sector_size_entry = {
>> .show = queue_logical_block_size_show,
>> };
>>
>> -QUEUE_RW_ENTRY(queue_rotational, "rotational");
>> -QUEUE_RW_ENTRY(queue_iostats, "iostats");
>> -QUEUE_RW_ENTRY(queue_add_random, "add_random");
>> -QUEUE_RW_ENTRY(queue_stable_writes, "stable_writes");
>> +QUEUE_LIM_RW_ENTRY(queue_rotational, "rotational");
>> +QUEUE_LIM_RW_ENTRY(queue_iostats, "iostats");
>> +QUEUE_LIM_RW_ENTRY(queue_add_random, "add_random");
>> +QUEUE_LIM_RW_ENTRY(queue_stable_writes, "stable_writes");
>>
>> #ifdef CONFIG_BLK_WBT
>> static ssize_t queue_var_store64(s64 *var, const char *page)
>> @@ -695,7 +676,7 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr,
>> struct request_queue *q = disk->queue;
>> ssize_t res;
>>
>> - if (!entry->store)
>> + if (!entry->store_limit && !entry->store)
>> return -EIO;
>>
>> /*
>> @@ -706,11 +687,24 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr,
>> if (entry->load_module)
>> entry->load_module(disk, page, length);
>>
>> - blk_mq_freeze_queue(q);
>> mutex_lock(&q->sysfs_lock);
>> - res = entry->store(disk, page, length);
>> - mutex_unlock(&q->sysfs_lock);
>> + blk_mq_freeze_queue(q);
>
> Order between freeze and ->sysfs_lock is changed, and it may cause new
> lockdep warning because we may freeze queue first before acquiring
> ->sysfs_lock in del_gendisk().
>
On contrary, in elevator_disable() and elevator_switch() we acquire
->sysfs_lock first before freezing the queue. I think this is a mess and
we need to fix ordering. We need to decide ordering rules. IMO, the
correct order should be to acquire ->sysfs_lock before freezing queue.
Likewise with this patch now we acquire ->limits_lock before freezing the
queue.

Thanks,
--Nilay