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BUG: KCSAN: data-race in __add_to_page_cache_locked / file_write_and_wait_range

write to 0xffff88813a441d20 of 8 bytes by task 2873 on cpu 1:
 __add_to_page_cache_locked+0x256/0x4e0 mm/filemap.c:914
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:967
 pagecache_get_page+0x6a3/0x900 mm/filemap.c:1896
 grab_cache_page_write_begin+0x3f/0x70 mm/filemap.c:3610
 ext4_da_write_begin+0x305/0x820 fs/ext4/inode.c:2984
 generic_perform_write+0x196/0x3a0 mm/filemap.c:3660
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813a441d20 of 8 bytes by task 2883 on cpu 0:
 mapping_needs_writeback mm/filemap.c:621 [inline]
 file_write_and_wait_range+0x48/0x210 mm/filemap.c:791
 ext4_sync_file+0x105/0x670 fs/ext4/fsync.c:151
 vfs_fsync_range fs/sync.c:200 [inline]
 vfs_fsync fs/sync.c:214 [inline]
 do_fsync fs/sync.c:224 [inline]
 __do_sys_fsync fs/sync.c:232 [inline]
 __se_sys_fsync fs/sync.c:230 [inline]
 __x64_sys_fsync+0x123/0x160 fs/sync.c:230
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 2883 Comm: syz-executor.1 Tainted: G        W         5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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