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BUG: KCSAN: data-race in ext4_da_write_end / ext4_writepages

write to 0xffff888106a11a88 of 8 bytes by task 6419 on cpu 1:
 mpage_map_and_submit_extent fs/ext4/inode.c:2507 [inline]
 ext4_writepages+0x13ca/0x1d10 fs/ext4/inode.c:2800
 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
 filemap_write_and_wait include/linux/fs.h:2897 [inline]
 ext4_bmap+0x124/0x230 fs/ext4/inode.c:3200
 bmap+0x56/0x80 fs/inode.c:1711
 ioctl_fibmap fs/ioctl.c:77 [inline]
 file_ioctl fs/ioctl.c:534 [inline]
 do_vfs_ioctl+0x1284/0x1410 fs/ioctl.c:1048
 __do_sys_ioctl fs/ioctl.c:1067 [inline]
 __se_sys_ioctl+0x83/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 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 0xffff888106a11a88 of 8 bytes by task 6411 on cpu 0:
 ext4_da_write_end+0xfc/0x730 fs/ext4/inode.c:3092
 generic_perform_write+0x22a/0x3c0 mm/filemap.c:3667
 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]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_writev fs/read_write.c:939 [inline]
 do_pwritev+0x1e5/0x3a0 fs/read_write.c:1036
 __do_sys_pwritev fs/read_write.c:1083 [inline]
 __se_sys_pwritev fs/read_write.c:1078 [inline]
 __x64_sys_pwritev+0x54/0x60 fs/read_write.c:1078
 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: 0x0000000000000000 -> 0x000000000412f000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6411 Comm: syz-executor.5 Not tainted 5.14.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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