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BUG: KCSAN: data-race in ext4_setattr / ondemand_readahead

write to 0xffff888120672238 of 8 bytes by task 7296 on cpu 0:
 i_size_write include/linux/fs.h:876 [inline]
 ext4_setattr+0xd63/0xec0 fs/ext4/inode.c:5386
 notify_change+0x7d7/0xa80 fs/attr.c:336
 do_truncate+0xe0/0x120 fs/open.c:64
 handle_truncate fs/namei.c:2909 [inline]
 do_open fs/namei.c:3255 [inline]
 path_openat+0x1a31/0x20a0 fs/namei.c:3368
 do_filp_open+0xbd/0x1d0 fs/namei.c:3395
 do_sys_openat2+0x33b/0x500 fs/open.c:1168
 do_sys_open fs/open.c:1184 [inline]
 __do_sys_creat fs/open.c:1258 [inline]
 __se_sys_creat fs/open.c:1252 [inline]
 __x64_sys_creat+0x62/0x80 fs/open.c:1252
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888120672238 of 8 bytes by task 7292 on cpu 1:
 i_size_read include/linux/fs.h:854 [inline]
 __do_page_cache_readahead mm/readahead.c:260 [inline]
 ra_submit mm/internal.h:64 [inline]
 ondemand_readahead+0x475/0x6e0 mm/readahead.c:551
 page_cache_sync_readahead+0x178/0x1a0 mm/readahead.c:585
 generic_file_buffered_read+0x2ec/0x1f60 mm/filemap.c:2199
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2503
 ext4_file_read_iter+0x2d8/0x420 fs/ext4/file.c:74
 call_read_iter include/linux/fs.h:1876 [inline]
 generic_file_splice_read+0x22b/0x310 fs/splice.c:312
 do_splice_to fs/splice.c:870 [inline]
 splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7292 Comm: syz-executor.4 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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