If blk-throttle is enabled and io is issued before blk_throtl_register_queue() is done. Divide by zero crash will be triggered in tg_may_dispatch() because 'throtl_slice' is uninitialized.

The problem is fixed in commit 75f4dca59694 ("block: call blk_register_queue earlier in device_add_disk") from mainline, however it's too hard to backport this patch due to lots of refactoring.

Thus introduce a new flag QUEUE_FLAG_THROTL_INIT_DONE. It will be set after blk_throtl_register_queue() is done, and will be checked before applying any config.

Signed-off-by: Yu Kuai yukuai3@huawei.com --- block/blk-sysfs.c | 2 ++ block/blk-throttle.c | 41 +++++++++++++++++++++++++++++++++++++++-- include/linux/blkdev.h | 1 + 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 07494deb1a26..7d250acf8ece 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -954,6 +954,7 @@ int blk_register_queue(struct gendisk *disk) blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q); wbt_enable_default(q); blk_throtl_register_queue(q); + blk_queue_flag_set(QUEUE_FLAG_THROTL_INIT_DONE, q);

/* Now everything is ready and send out KOBJ_ADD uevent */ kobject_uevent(&q->kobj, KOBJ_ADD); @@ -986,6 +987,7 @@ void blk_unregister_queue(struct gendisk *disk) if (!blk_queue_registered(q)) return;

+ blk_queue_flag_clear(QUEUE_FLAG_THROTL_INIT_DONE, q); /* * Since sysfs_remove_dir() prevents adding new directory entries * before removal of existing entries starts, protect against diff --git a/block/blk-throttle.c b/block/blk-throttle.c index caee658609d7..b2eeca9a9962 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -11,6 +11,8 @@ #include <linux/bio.h> #include <linux/blktrace_api.h> #include <linux/blk-cgroup.h> +#include <linux/sched/signal.h> +#include <linux/delay.h> #include "blk.h"

/* Max dispatch from a group in 1 round */ @@ -1428,6 +1430,31 @@ static void tg_conf_updated(struct throtl_grp *tg, bool global) } }

+static inline int throtl_check_init_done(struct request_queue *q) +{ + if (test_bit(QUEUE_FLAG_THROTL_INIT_DONE, &q->queue_flags)) + return 0; + + return blk_queue_dying(q) ? -ENODEV : -EBUSY; +} + +/* + * If throtl_check_init_done() return -EBUSY, we should retry after a short + * msleep(), since that throttle init will be completed in blk_register_queue() + * soon. + */ +static inline int throtl_restart_syscall_when_busy(int errno) +{ + int ret = errno; + + if (ret == -EBUSY) { + msleep(10); + ret = restart_syscall(); + } + + return ret; +} + static ssize_t tg_set_conf(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off, bool is_u64) { @@ -1441,6 +1468,10 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of, if (ret) return ret;

+ ret = throtl_check_init_done(ctx.disk->queue); + if (ret) + goto out_finish; + ret = -EINVAL; if (sscanf(ctx.body, "%llu", &v) != 1) goto out_finish; @@ -1448,7 +1479,6 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of, v = U64_MAX;

tg = blkg_to_tg(ctx.blkg); - if (is_u64) *(u64 *)((void *)tg + of_cft(of)->private) = v; else @@ -1458,6 +1488,8 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of, ret = 0; out_finish: blkg_conf_finish(&ctx); + ret = throtl_restart_syscall_when_busy(ret); + return ret ?: nbytes; }

@@ -1607,8 +1639,11 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of, if (ret) return ret;

- tg = blkg_to_tg(ctx.blkg); + ret = throtl_check_init_done(ctx.disk->queue); + if (ret) + goto out_finish;

+ tg = blkg_to_tg(ctx.blkg); v[0] = tg->bps_conf[READ][index]; v[1] = tg->bps_conf[WRITE][index]; v[2] = tg->iops_conf[READ][index]; @@ -1704,6 +1739,8 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of, ret = 0; out_finish: blkg_conf_finish(&ctx); + ret = throtl_restart_syscall_when_busy(ret); + return ret ?: nbytes; }

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 209ba8e7bd31..22be9f090bf1 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -684,6 +684,7 @@ struct request_queue { #define QUEUE_FLAG_NOMERGES 5 /* disable merge attempts */ #define QUEUE_FLAG_SAME_COMP 6 /* complete on same CPU-group */ #define QUEUE_FLAG_FAIL_IO 7 /* fake timeout */ +#define QUEUE_FLAG_THROTL_INIT_DONE 8 /* io throttle can be online */ #define QUEUE_FLAG_NONROT 9 /* non-rotational device (SSD) */ #define QUEUE_FLAG_VIRT QUEUE_FLAG_NONROT /* paravirt device */ #define QUEUE_FLAG_IO_STAT 10 /* do IO stats */