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BUG: KCSAN: data-race in __add_to_page_cache_locked / ext4_writepages

write to 0xffff88816ba4a400 of 8 bytes by task 16705 on cpu 0:
 __add_to_page_cache_locked+0x256/0x4b0 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+0x196/0x3c0 mm/filemap.c:3656
 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]
 aio_write+0x287/0x360 fs/aio.c:1578
 __io_submit_one fs/aio.c:1837 [inline]
 io_submit_one+0x82f/0x1350 fs/aio.c:1880
 __do_sys_io_submit fs/aio.c:1939 [inline]
 __se_sys_io_submit+0xf5/0x260 fs/aio.c:1909
 __x64_sys_io_submit+0x3f/0x50 fs/aio.c:1909
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88816ba4a400 of 8 bytes by task 16714 on cpu 1:
 ext4_writepages+0x111/0x1d10 fs/ext4/inode.c:2668
 do_writepages+0x7b/0x150 mm/page-writeback.c:2355
 __filemap_fdatawrite_range mm/filemap.c:413 [inline]
 filemap_write_and_wait_range+0x20a/0x390 mm/filemap.c:686
 ext4_punch_hole+0x142/0x9a0 fs/ext4/inode.c:4020
 ext4_fallocate+0xea/0x4d0 fs/ext4/extents.c:4662
 vfs_fallocate+0x463/0x660 fs/open.c:311
 ksys_fallocate fs/open.c:334 [inline]
 __do_sys_fallocate fs/open.c:342 [inline]
 __se_sys_fallocate fs/open.c:340 [inline]
 __x64_sys_fallocate+0x75/0xc0 fs/open.c:340
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000061 -> 0x0000000000000062

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16714 Comm: syz-executor.4 Not tainted 5.14.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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