syzbot

loop2: detected capacity change from 0 to 128
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BUG: KCSAN: data-race in filemap_fault / generic_write_end

write to 0xffff88813a89ca00 of 8 bytes by task 19739 on cpu 1:
 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
 cont_expand_zero fs/buffer.c:2514 [inline]
 cont_write_begin+0x2c0/0x690 fs/buffer.c:2572
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 generic_cont_expand_simple+0xa7/0x140 fs/buffer.c:2473
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_fallocate+0x182/0x1d0 fs/fat/file.c:301
 vfs_fallocate+0x378/0x3e0 fs/open.c:324
 ksys_fallocate fs/open.c:347 [inline]
 __do_sys_fallocate fs/open.c:355 [inline]
 __se_sys_fallocate fs/open.c:353 [inline]
 __x64_sys_fallocate+0x79/0xc0 fs/open.c:353
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88813a89ca00 of 8 bytes by task 19735 on cpu 0:
 i_size_read include/linux/fs.h:910 [inline]
 filemap_fault+0x91/0xc30 mm/filemap.c:3209
 __do_fault mm/memory.c:4265 [inline]
 do_read_fault mm/memory.c:4628 [inline]
 do_fault mm/memory.c:4762 [inline]
 do_pte_missing mm/memory.c:3730 [inline]
 handle_pte_fault mm/memory.c:5038 [inline]
 __handle_mm_fault mm/memory.c:5179 [inline]
 handle_mm_fault+0x13bd/0x2dd0 mm/memory.c:5344
 faultin_page mm/gup.c:956 [inline]
 __get_user_pages+0x402/0xe40 mm/gup.c:1239
 populate_vma_page_range mm/gup.c:1677 [inline]
 __mm_populate+0x216/0x330 mm/gup.c:1786
 mm_populate include/linux/mm.h:3379 [inline]
 vm_mmap_pgoff+0x1a7/0x240 mm/util.c:551
 ksys_mmap_pgoff+0x2b8/0x330 mm/mmap.c:1425
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x0000000000012000 -> 0x0000000000014000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19735 Comm: syz-executor.2 Not tainted 6.6.0-syzkaller-12715-g6bdfe2d88b9f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
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