==================================================================
BUG: KCSAN: data-race in blk_mq_rq_ctx_init / blk_mq_rq_ctx_init

read to 0xffff8881027c4550 of 8 bytes by task 3353 on cpu 1:
 blk_mq_rq_ctx_init+0x3ca/0x4e0 block/blk-mq.c:351
 __blk_mq_alloc_request+0x270/0x290 block/blk-mq.c:406
 blk_mq_submit_bio+0x27f/0xec0 block/blk-mq.c:2206
 __submit_bio+0x41a/0x480 block/blk-core.c:929
 __submit_bio_noacct_mq block/blk-core.c:1009 [inline]
 submit_bio_noacct+0x46d/0x530 block/blk-core.c:1039
 submit_bio+0x10c/0x190
 ext4_mpage_readpages+0x10f2/0x1140 fs/ext4/readpage.c:411
 ext4_readahead+0x99/0xa0 fs/ext4/inode.c:3202
 read_pages+0xb6/0x540 mm/readahead.c:130
 page_cache_ra_unbounded+0x3d2/0x430 mm/readahead.c:239
 ondemand_readahead+0x58c/0x7c0
 page_cache_sync_ra+0xaf/0xe0 mm/readahead.c:580
 page_cache_sync_readahead include/linux/pagemap.h:883 [inline]
 filemap_get_pages mm/filemap.c:2545 [inline]
 filemap_read+0x3ad/0x1220 mm/filemap.c:2628
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2779
 ext4_file_read_iter+0x1db/0x290
 call_read_iter include/linux/fs.h:2157 [inline]
 generic_file_splice_read+0x24f/0x330 fs/splice.c:311
 do_splice_to fs/splice.c:796 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:870
 do_splice_direct+0x106/0x190 fs/splice.c:979
 do_sendfile+0x63e/0xbb0 fs/read_write.c:1249
 __do_sys_sendfile64 fs/read_write.c:1314 [inline]
 __se_sys_sendfile64 fs/read_write.c:1300 [inline]
 __x64_sys_sendfile64+0x102/0x140 fs/read_write.c:1300
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

write to 0xffff8881027c4550 of 8 bytes by task 3347 on cpu 0:
 blk_mq_rq_ctx_init+0x3dc/0x4e0 block/blk-mq.c:351
 __blk_mq_alloc_request+0x270/0x290 block/blk-mq.c:406
 blk_mq_submit_bio+0x27f/0xec0 block/blk-mq.c:2206
 __submit_bio+0x41a/0x480 block/blk-core.c:929
 __submit_bio_noacct_mq block/blk-core.c:1009 [inline]
 submit_bio_noacct+0x46d/0x530 block/blk-core.c:1039
 submit_bio+0x10c/0x190
 ext4_mpage_readpages+0x10f2/0x1140 fs/ext4/readpage.c:411
 ext4_readahead+0x99/0xa0 fs/ext4/inode.c:3202
 read_pages+0xb6/0x540 mm/readahead.c:130
 page_cache_ra_unbounded+0x3d2/0x430 mm/readahead.c:239
 ondemand_readahead+0x58c/0x7c0
 page_cache_sync_ra+0xaf/0xe0 mm/readahead.c:580
 page_cache_sync_readahead include/linux/pagemap.h:883 [inline]
 filemap_get_pages mm/filemap.c:2545 [inline]
 filemap_read+0x3ad/0x1220 mm/filemap.c:2628
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2779
 ext4_file_read_iter+0x1db/0x290
 call_read_iter include/linux/fs.h:2157 [inline]
 generic_file_splice_read+0x24f/0x330 fs/splice.c:311
 do_splice_to fs/splice.c:796 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:870
 do_splice_direct+0x106/0x190 fs/splice.c:979
 do_sendfile+0x63e/0xbb0 fs/read_write.c:1249
 __do_sys_sendfile64 fs/read_write.c:1314 [inline]
 __se_sys_sendfile64 fs/read_write.c:1300 [inline]
 __x64_sys_sendfile64+0x102/0x140 fs/read_write.c:1300
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000a63 -> 0x0000000000000a64

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3347 Comm: syz-executor.2 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
syz-executor.2 (3347) used greatest stack depth: 10112 bytes left