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BUG: KCSAN: data-race in __add_to_page_cache_locked / ext4_writepages

write to 0xffff888125512378 of 8 bytes by task 11140 on cpu 1:
 __add_to_page_cache_locked+0x298/0x780 mm/filemap.c:868
 add_to_page_cache_lru+0xc4/0x260 mm/filemap.c:921
 pagecache_get_page+0x2ac/0x6f0 mm/filemap.c:1660
 grab_cache_page_write_begin+0x5d/0x90 mm/filemap.c:3237
 ext4_da_write_begin+0x1a3/0x840 fs/ext4/inode.c:2966
 generic_perform_write+0x136/0x320 mm/filemap.c:3287
 ext4_buffered_write_iter+0x143/0x290 fs/ext4/file.c:270
 ext4_file_write_iter+0xfa/0xd70 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888125512378 of 8 bytes by task 11146 on cpu 0:
 ext4_writepages+0x181/0x1d40 fs/ext4/inode.c:2639
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1c5/0x230 mm/filemap.c:421
 filemap_write_and_wait_range mm/filemap.c:654 [inline]
 filemap_write_and_wait_range+0xb1/0x150 mm/filemap.c:648
 ext4_punch_hole+0x813/0xab0 fs/ext4/inode.c:3957
 ext4_fallocate+0x28b/0x21a0 fs/ext4/extents.c:4865
 vfs_fallocate+0x3be/0x650 fs/open.c:309
 ioctl_preallocate+0x12b/0x190 fs/ioctl.c:504
 file_ioctl fs/ioctl.c:547 [inline]
 do_vfs_ioctl+0xa59/0xd00 fs/ioctl.c:742
 ksys_ioctl+0xbd/0x150 fs/ioctl.c:761
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:770
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11146 Comm: syz-executor.3 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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