From: Tao Cui Writing a multiple of 2^32 (e.g. 4294967296) to a legacy cgroup v1 throttle iops file (blkio.throttle.{read,write}_iops_device) silently truncates to 0: tg_set_conf() stores the sscanf-parsed u64 value into an unsigned int field with no clamping. The cgroup v2 path, tg_set_limit(), already clamps the same kind of value with min_t(u64, val, UINT_MAX), but the legacy path never did. Note that the "!v -> U64_MAX" mapping only catches an explicit zero and does not catch a value that truncates to zero. With iops stored as 0, tg_update_has_rules() sets has_rules_iops[] and the next IO reaches tg_within_iops_limit(), which computes jiffy_wait = max(jiffy_wait, HZ / iops_limit + 1); triggering a divide-by-zero oops. Fix it in two places: * tg_set_conf(): clamp the value to UINT_MAX, consistent with tg_set_limit(). This closes the truncation root cause (and the general silent truncation for any value above UINT_MAX). * tg_dispatch_iops_time(): treat iops_limit == 0 as unlimited so the divide in tg_within_iops_limit() is never reached, defending against any future path that could produce a zero limit. Signed-off-by: Tao Cui --- block/blk-throttle.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index ffc3b70065d4..3f3c1374f4b2 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -883,7 +883,12 @@ static unsigned long tg_dispatch_iops_time(struct throtl_grp *tg, struct bio *bi u32 iops_limit = tg_iops_limit(tg, rw); unsigned long iops_wait; - if (iops_limit == UINT_MAX || tg->flags & THROTL_TG_CANCELING) + /* + * iops_limit == 0 is not a valid limit. Treat it as unlimited so we + * never reach the HZ / iops_limit divide in tg_within_iops_limit(). + */ + if (iops_limit == UINT_MAX || iops_limit == 0 || + tg->flags & THROTL_TG_CANCELING) return 0; tg_update_slice(tg, rw); @@ -1386,7 +1391,8 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of, if (is_u64) *(u64 *)((void *)tg + of_cft(of)->private) = v; else - *(unsigned int *)((void *)tg + of_cft(of)->private) = v; + *(unsigned int *)((void *)tg + of_cft(of)->private) = + min_t(u64, v, UINT_MAX); tg_conf_updated(tg, false); ret = 0; -- 2.43.0