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BUG: KCSAN: data-race in ondemand_readahead / read_pages

read to 0xffff888121b5b784 of 4 bytes by task 9380 on cpu 1:
 read_pages+0x266/0x560 mm/readahead.c:171
 page_cache_ra_unbounded+0x2a9/0x2e0 mm/readahead.c:269
 do_page_cache_ra mm/readahead.c:299 [inline]
 page_cache_ra_order mm/readahead.c:559 [inline]
 ondemand_readahead+0x550/0x6c0 mm/readahead.c:681
 page_cache_sync_ra+0x284/0x2a0 mm/readahead.c:708
 page_cache_sync_readahead include/linux/pagemap.h:1213 [inline]
 filemap_get_pages+0x254/0xea0 mm/filemap.c:2563
 filemap_splice_read+0x23a/0x810 mm/filemap.c:2925
 ext4_file_splice_read+0x95/0xb0 fs/ext4/file.c:158
 vfs_splice_read fs/splice.c:994 [inline]
 splice_direct_to_actor+0x28c/0x690 fs/splice.c:1070
 do_splice_direct+0x10d/0x190 fs/splice.c:1195
 do_sendfile+0x3b6/0x9a0 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64 fs/read_write.c:1308 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffff888121b5b784 of 4 bytes by task 9381 on cpu 0:
 ondemand_readahead+0x346/0x6c0 mm/readahead.c:660
 page_cache_sync_ra+0x284/0x2a0 mm/readahead.c:708
 page_cache_sync_readahead include/linux/pagemap.h:1213 [inline]
 filemap_get_pages+0x254/0xea0 mm/filemap.c:2563
 filemap_splice_read+0x23a/0x810 mm/filemap.c:2925
 ext4_file_splice_read+0x95/0xb0 fs/ext4/file.c:158
 vfs_splice_read fs/splice.c:994 [inline]
 splice_direct_to_actor+0x28c/0x690 fs/splice.c:1070
 do_splice_direct+0x10d/0x190 fs/splice.c:1195
 do_sendfile+0x3b6/0x9a0 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64 fs/read_write.c:1308 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000003 -> 0x00000002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9381 Comm: syz-executor.4 Not tainted 6.4.0-syzkaller-08686-ge55e5df193d2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
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