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BUG: KCSAN: data-race in __filemap_add_folio / nr_blockdev_pages

read-write to 0xffff888102455678 of 8 bytes by task 29399 on cpu 1:
 __filemap_add_folio+0x385/0x730 mm/filemap.c:904
 filemap_add_folio+0x6f/0x150 mm/filemap.c:939
 __filemap_get_folio+0x313/0x500 mm/filemap.c:1976
 pagecache_get_page+0x2a/0xb0 mm/folio-compat.c:99
 find_or_create_page include/linux/pagemap.h:635 [inline]
 grow_dev_page fs/buffer.c:995 [inline]
 grow_buffers fs/buffer.c:1060 [inline]
 __getblk_slow fs/buffer.c:1087 [inline]
 __getblk_gfp+0x17c/0x8d0 fs/buffer.c:1382
 sb_getblk_gfp include/linux/buffer_head.h:372 [inline]
 __ext4_sb_bread_gfp+0x46/0x170 fs/ext4/super.c:229
 ext4_sb_bread_unmovable fs/ext4/super.c:252 [inline]
 ext4_load_super fs/ext4/super.c:5033 [inline]
 __ext4_fill_super fs/ext4/super.c:5213 [inline]
 ext4_fill_super+0x449/0x38f0 fs/ext4/super.c:5672
 get_tree_bdev+0x2a8/0x3a0 fs/super.c:1303
 ext4_get_tree+0x1c/0x20 fs/ext4/super.c:5704
 vfs_get_tree+0x51/0x190 fs/super.c:1510
 do_new_mount+0x200/0x650 fs/namespace.c:3039
 path_mount+0x498/0xb40 fs/namespace.c:3369
 do_mount fs/namespace.c:3382 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount+0x27f/0x2d0 fs/namespace.c:3568
 __x64_sys_mount+0x67/0x80 fs/namespace.c:3568
 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

read to 0xffff888102455678 of 8 bytes by task 29408 on cpu 0:
 nr_blockdev_pages+0x7f/0xd0 block/bdev.c:457
 si_meminfo+0x3e/0x60 mm/page_alloc.c:5197
 handshake_net_init+0x7a/0x140 net/handshake/netlink.c:212
 ops_init+0x1fc/0x2c0 net/core/net_namespace.c:136
 setup_net+0x2b5/0x700 net/core/net_namespace.c:339
 copy_net_ns+0x36c/0x500 net/core/net_namespace.c:491
 create_new_namespaces+0x228/0x430 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xe4/0x120 kernel/nsproxy.c:228
 ksys_unshare+0x38d/0x6d0 kernel/fork.c:3444
 __do_sys_unshare kernel/fork.c:3515 [inline]
 __se_sys_unshare kernel/fork.c:3513 [inline]
 __x64_sys_unshare+0x1f/0x30 kernel/fork.c:3513
 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: 0x0000000000000000 -> 0x0000000000000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 29408 Comm: syz-executor.0 Not tainted 6.4.0-rc3-syzkaller-00017-g9d646009f65d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/16/2023
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