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BUG: KCSAN: data-race in ondemand_readahead / ondemand_readahead

write to 0xffff888103eda7a4 of 4 bytes by task 14346 on cpu 1:
 ondemand_readahead+0x335/0x7a0 mm/readahead.c:528
 page_cache_sync_ra+0x95/0xd0 mm/readahead.c:577
 page_cache_sync_readahead include/linux/pagemap.h:840 [inline]
 filemap_get_pages mm/filemap.c:2375 [inline]
 filemap_read+0x380/0x1210 mm/filemap.c:2458
 generic_file_read_iter+0x84/0x3e0 mm/filemap.c:2609
 ext4_file_read_iter+0x1db/0x290 fs/ext4/file.c:73
 call_read_iter include/linux/fs.h:1971 [inline]
 generic_file_splice_read+0x22a/0x310 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+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888103eda7a4 of 4 bytes by task 14329 on cpu 0:
 ondemand_readahead+0x192/0x7a0 mm/readahead.c:462
 page_cache_async_ra+0x16e/0x190 mm/readahead.c:607
 page_cache_async_readahead include/linux/pagemap.h:863 [inline]
 filemap_readahead mm/filemap.c:2350 [inline]
 filemap_get_pages mm/filemap.c:2391 [inline]
 filemap_read+0x485/0x1210 mm/filemap.c:2458
 generic_file_read_iter+0x84/0x3e0 mm/filemap.c:2609
 ext4_file_read_iter+0x1db/0x290 fs/ext4/file.c:73
 call_read_iter include/linux/fs.h:1971 [inline]
 generic_file_splice_read+0x22a/0x310 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+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 14329 Comm: syz-executor.3 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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