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BUG: KCSAN: data-race in ondemand_readahead / ondemand_readahead

read to 0xffff888158e1cca0 of 4 bytes by task 22109 on cpu 0:
 ondemand_readahead+0x121/0x700 mm/readahead.c:464
 page_cache_async_ra+0xb5/0xe0 mm/readahead.c:608
 do_async_mmap_readahead+0x1f5/0x230 mm/filemap.c:3053
 filemap_fault+0x100/0x8b0 mm/filemap.c:3107
 __do_fault mm/memory.c:3868 [inline]
 do_read_fault mm/memory.c:4183 [inline]
 do_fault mm/memory.c:4312 [inline]
 handle_pte_fault mm/memory.c:4570 [inline]
 __handle_mm_fault mm/memory.c:4705 [inline]
 handle_mm_fault+0xba6/0x1590 mm/memory.c:4803
 do_user_addr_fault+0x617/0xb90 arch/x86/mm/fault.c:1397
 handle_page_fault arch/x86/mm/fault.c:1484 [inline]
 exc_page_fault+0x91/0x290 arch/x86/mm/fault.c:1540
 asm_exc_page_fault+0x1e/0x30
 fault_in_readable+0x115/0x1a0
 fault_in_iov_iter_readable+0xd7/0x140 lib/iov_iter.c:458
 generic_perform_write+0xf2/0x400 mm/filemap.c:3755
 ext4_buffered_write_iter+0x19d/0x290 fs/ext4/file.c:268
 ext4_file_write_iter+0x227/0xda0
 call_write_iter include/linux/fs.h:2074 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x7f5/0x950 fs/read_write.c:590
 ksys_write+0xd9/0x190 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:652
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

write to 0xffff888158e1cca0 of 4 bytes by task 22110 on cpu 1:
 ondemand_readahead+0x337/0x700
 page_cache_async_ra+0xb5/0xe0 mm/readahead.c:608
 do_async_mmap_readahead+0x1f5/0x230 mm/filemap.c:3053
 filemap_fault+0x100/0x8b0 mm/filemap.c:3107
 __do_fault mm/memory.c:3868 [inline]
 do_read_fault mm/memory.c:4183 [inline]
 do_fault mm/memory.c:4312 [inline]
 handle_pte_fault mm/memory.c:4570 [inline]
 __handle_mm_fault mm/memory.c:4705 [inline]
 handle_mm_fault+0xba6/0x1590 mm/memory.c:4803
 faultin_page mm/gup.c:969 [inline]
 __get_user_pages+0x342/0xc10 mm/gup.c:1190
 populate_vma_page_range mm/gup.c:1522 [inline]
 __mm_populate+0x24d/0x370 mm/gup.c:1631
 mm_populate include/linux/mm.h:2702 [inline]
 vm_mmap_pgoff+0x160/0x1f0 mm/util.c:524
 ksys_mmap_pgoff+0x265/0x320 mm/mmap.c:1630
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000040 -> 0x00000020

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22110 Comm: syz-executor.5 Tainted: G        W         5.17.0-syzkaller-00192-geaa54b1458ca-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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