A recent commit made cpumask_next*() trigger a warning when passed
n = nr_cpu_ids - 1. This means extra care must be taken when feeding CPU
numbers back into cpumask_next*().
The warning occurs nearly every boot on QEMU:
[ 5.398453] WARNING: CPU: 3 PID: 162 at include/linux/cpumask.h:110 __blk_mq_delay_run_hw_queue+0x16b/0x180
[ 5.399317] Modules linked in:
[ 5.399646] CPU: 3 PID: 162 Comm: ssh-keygen Tainted: G N 6.0.0-rc4-00004-g93003cb24006 #55
[ 5.400135] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 5.405430] Call Trace:
[ 5.406152] <TASK>
[ 5.406452] blk_mq_sched_insert_requests+0x67/0x150
[ 5.406759] blk_mq_flush_plug_list+0xd0/0x280
[ 5.406987] ? bit_wait+0x60/0x60
[ 5.407317] __blk_flush_plug+0xdb/0x120
[ 5.407561] ? bit_wait+0x60/0x60
[ 5.407765] io_schedule_prepare+0x38/0x40
[ 5.407974] io_schedule+0x6/0x40
[ 5.408283] bit_wait_io+0x8/0x60
[ 5.408485] __wait_on_bit+0x72/0x90
[ 5.408668] out_of_line_wait_on_bit+0x8c/0xb0
[ 5.408879] ? swake_up_one+0x30/0x30
[ 5.409158] ext4_read_bh+0x7a/0x80
[ 5.409381] ext4_get_branch+0xc0/0x130
[ 5.409583] ext4_ind_map_blocks+0x1ac/0xb30
[ 5.409844] ? __es_remove_extent+0x61/0x6d0
[ 5.410128] ? blk_account_io_merge_bio+0x67/0xd0
[ 5.410416] ? percpu_counter_add_batch+0x59/0xb0
[ 5.410720] ? percpu_counter_add_batch+0x59/0xb0
[ 5.410949] ? _raw_read_unlock+0x13/0x30
[ 5.411323] ext4_map_blocks+0xc2/0x590
[ 5.411609] ? xa_load+0x7c/0xa0
[ 5.411859] ext4_mpage_readpages+0x4a2/0xaa0
[ 5.412192] read_pages+0x69/0x2b0
[ 5.412477] ? folio_add_lru+0x4f/0x70
[ 5.412696] page_cache_ra_unbounded+0x11d/0x170
[ 5.412960] filemap_get_pages+0x109/0x5d0
[ 5.413340] ? __vma_adjust+0x348/0x930
[ 5.413576] filemap_read+0xb7/0x380
[ 5.413805] ? vma_merge+0x2e9/0x330
[ 5.414067] ? vma_set_page_prot+0x43/0x80
[ 5.414309] ? __inode_security_revalidate+0x5e/0x80
[ 5.414581] ? selinux_file_permission+0x107/0x130
[ 5.414889] vfs_read+0x205/0x2e0
[ 5.415162] ksys_read+0x54/0xd0
[ 5.415348] do_syscall_64+0x3a/0x90
[ 5.415584] entry_SYSCALL_64_after_hwframe+0x63/0xcd
Fixes: 78e5a3399421 ("cpumask: fix checking valid cpu range")
Suggested-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx>
---
block/blk-mq.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c96c8c4f751b..30ae51eda95e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2046,8 +2046,13 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
if (--hctx->next_cpu_batch <= 0) {
select_cpu:
- next_cpu = cpumask_next_and(next_cpu, hctx->cpumask,
- cpu_online_mask);
+ if (next_cpu == nr_cpu_ids - 1)
+ next_cpu = nr_cpu_ids;
+ else
+ next_cpu = cpumask_next_and(next_cpu,
+ hctx->cpumask,
+ cpu_online_mask);
+
if (next_cpu >= nr_cpu_ids)
next_cpu = blk_mq_first_mapped_cpu(hctx);
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
--
2.31.1
