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| author | Tejun Heo <tj@kernel.org> | 2020-09-11 18:40:49 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2020-09-11 16:41:47 -0600 |
| commit | 769b628de0b9a7ab0b81e6eecca5ee7bf66e978d (patch) | |
| tree | 39ebaa9dc4a2a062fe38ea3aebfdce8d1c642cc9 /block | |
| parent | 0806e60f31ec10822cd230d12603169d1bb7840e (diff) | |
| download | linux-769b628de0b9a7ab0b81e6eecca5ee7bf66e978d.tar.gz linux-769b628de0b9a7ab0b81e6eecca5ee7bf66e978d.tar.bz2 linux-769b628de0b9a7ab0b81e6eecca5ee7bf66e978d.zip | |
blk-iocost: fix divide-by-zero in transfer_surpluses()
Conceptually, root_iocg->hweight_donating must be less than WEIGHT_ONE but
all hweight calculations round up and thus it may end up >= WEIGHT_ONE
triggering divide-by-zero and other issues. Bound the value to avoid
surprises.
Fixes: e08d02aa5fc9 ("blk-iocost: implement Andy's method for donation weight updates")
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-iocost.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index fc897bb142bc..6e29b4dcf356 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1881,15 +1881,21 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) /* * Calculate the global donation rate (gamma) - the rate to adjust - * non-donating budgets by. No need to use 64bit multiplication here as - * the first operand is guaranteed to be smaller than WEIGHT_ONE - * (1<<16). + * non-donating budgets by. + * + * No need to use 64bit multiplication here as the first operand is + * guaranteed to be smaller than WEIGHT_ONE (1<<16). + * + * We know that there are beneficiary nodes and the sum of the donating + * hweights can't be whole; however, due to the round-ups during hweight + * calculations, root_iocg->hweight_donating might still end up equal to + * or greater than whole. Limit the range when calculating the divider. * * gamma = (1 - t_r') / (1 - t_r) */ gamma = DIV_ROUND_UP( (WEIGHT_ONE - root_iocg->hweight_after_donation) * WEIGHT_ONE, - WEIGHT_ONE - root_iocg->hweight_donating); + WEIGHT_ONE - min_t(u32, root_iocg->hweight_donating, WEIGHT_ONE - 1)); /* * Calculate adjusted hwi, child_adjusted_sum and inuse for the inner |