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BUG: KCSAN: data-race in __mpage_writepage / generic_write_end

write to 0xffff8881368a6850 of 8 bytes by task 7548 on cpu 1:
 i_size_write include/linux/fs.h:932 [inline]
 generic_write_end+0x94/0x230 fs/buffer.c:2275
 fat_write_end+0x4e/0x160 fs/fat/inode.c:244
 cont_expand_zero fs/buffer.c:2497 [inline]
 cont_write_begin+0x2c0/0x690 fs/buffer.c:2555
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 generic_cont_expand_simple+0xa7/0x140 fs/buffer.c:2456
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_setattr+0x2a9/0x840 fs/fat/file.c:513
 notify_change+0x866/0x8e0 fs/attr.c:499
 do_truncate+0x116/0x150 fs/open.c:66
 do_sys_ftruncate+0x2ba/0x3b0 fs/open.c:194
 __do_sys_ftruncate fs/open.c:205 [inline]
 __se_sys_ftruncate fs/open.c:203 [inline]
 __x64_sys_ftruncate+0x33/0x40 fs/open.c:203
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff8881368a6850 of 8 bytes by task 7553 on cpu 0:
 i_size_read include/linux/fs.h:910 [inline]
 __mpage_writepage+0xa6/0xdc0 fs/mpage.c:478
 write_cache_pages+0x38d/0x740 mm/page-writeback.c:2474
 mpage_writepages+0x72/0xe0 fs/mpage.c:672
 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:388
 __filemap_fdatawrite_range+0xa1/0xd0 mm/filemap.c:421
 sync_file_range+0x1b3/0x220 fs/sync.c:292
 ksys_sync_file_range fs/sync.c:364 [inline]
 __do_sys_sync_file_range fs/sync.c:373 [inline]
 __se_sys_sync_file_range fs/sync.c:370 [inline]
 __x64_sys_sync_file_range+0x80/0xd0 fs/sync.c:370
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x0000000000cb6000 -> 0x0000000000cb8000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7553 Comm: syz-executor.1 Not tainted 6.8.0-rc1-syzkaller-00024-g5d9248eed480 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
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