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BUG: KCSAN: data-race in ext4_setattr / ondemand_readahead

write to 0xffff888134dfcbc0 of 8 bytes by task 23252 on cpu 1:
 i_size_write include/linux/fs.h:872 [inline]
 ext4_setattr+0xd54/0xec0 fs/ext4/inode.c:5483
 notify_change+0x8a3/0xa80 fs/attr.c:398
 do_truncate+0xe8/0x130 fs/open.c:64
 handle_truncate fs/namei.c:3020 [inline]
 do_open fs/namei.c:3371 [inline]
 path_openat+0x1a79/0x20b0 fs/namei.c:3500
 do_filp_open+0xd9/0x1f0 fs/namei.c:3527
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_creat fs/open.c:1277 [inline]
 __se_sys_creat fs/open.c:1271 [inline]
 __x64_sys_creat+0x62/0x80 fs/open.c:1271
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888134dfcbc0 of 8 bytes by task 23231 on cpu 0:
 i_size_read include/linux/fs.h:850 [inline]
 do_page_cache_ra mm/readahead.c:254 [inline]
 ondemand_readahead+0x511/0x7a0 mm/readahead.c:549
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23231 Comm: syz-executor.4 Tainted: G        W         5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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