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BUG: KCSAN: data-race in __mpage_writepage / generic_write_end

write to 0xffff88813bd7ca00 of 8 bytes by task 27254 on cpu 0:
 i_size_write include/linux/fs.h:932 [inline]
 generic_write_end+0x94/0x230 fs/buffer.c:2291
 fat_write_end+0x4e/0x160 fs/fat/inode.c:244
 generic_perform_write+0x267/0x410 mm/filemap.c:3938
 __generic_file_write_iter+0xa1/0x120 mm/filemap.c:4022
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4048
 call_write_iter include/linux/fs.h:2020 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x48a/0x790 fs/read_write.c:584
 ksys_write+0xeb/0x1a0 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:646
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88813bd7ca00 of 8 bytes by task 27272 on cpu 1:
 i_size_read include/linux/fs.h:910 [inline]
 __mpage_writepage+0xc0/0xd90 fs/mpage.c:488
 write_cache_pages+0x38d/0x740 mm/page-writeback.c:2474
 mpage_writepages+0x72/0xe0 fs/mpage.c:678
 fat_writepages+0x24/0x30 fs/fat/inode.c:200
 do_writepages+0x1c2/0x340 mm/page-writeback.c:2553
 filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:387
 __filemap_fdatawrite_range mm/filemap.c:420 [inline]
 file_write_and_wait_range+0xf4/0x190 mm/filemap.c:778
 __generic_file_fsync+0x4c/0x140 fs/libfs.c:1448
 fat_file_fsync+0x4c/0x100 fs/fat/file.c:191
 vfs_fsync_range fs/sync.c:188 [inline]
 vfs_fsync fs/sync.c:202 [inline]
 do_fsync fs/sync.c:212 [inline]
 __do_sys_fdatasync fs/sync.c:225 [inline]
 __se_sys_fdatasync fs/sync.c:223 [inline]
 __x64_sys_fdatasync+0x84/0xd0 fs/sync.c:223
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x000000000006f000 -> 0x000000000006febd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 27272 Comm: syz-executor.5 Not tainted 6.7.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
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