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BUG: KCSAN: data-race in rcu_gp_fqs_loop / rcu_preempt_deferred_qs_irqrestore

write to 0xffffffff85c7d0d0 of 8 bytes by task 19828 on cpu 1:
 rcu_preempt_deferred_qs_irqrestore+0x43d/0x580 kernel/rcu/tree_plugin.h:496
 rcu_read_unlock_special kernel/rcu/tree_plugin.h:644 [inline]
 __rcu_read_unlock+0x16a/0x3d0 kernel/rcu/tree_plugin.h:383
 rcu_read_unlock include/linux/rcupdate.h:670 [inline]
 find_get_entry+0x203/0x330 mm/filemap.c:1557
 pagecache_get_page+0x46/0x6f0 mm/filemap.c:1635
 find_get_page_flags include/linux/pagemap.h:266 [inline]
 ext4_mb_load_buddy_gfp+0x1e1/0xb00 fs/ext4/mballoc.c:1146
 ext4_mb_load_buddy fs/ext4/mballoc.c:1241 [inline]
 ext4_mb_find_by_goal+0x1ba/0x770 fs/ext4/mballoc.c:1832
 ext4_mb_regular_allocator+0xfd/0x9d0 fs/ext4/mballoc.c:2118
 ext4_mb_new_blocks+0xf6f/0x1de0 fs/ext4/mballoc.c:4539
 ext4_ext_map_blocks+0x1c0f/0x2320 fs/ext4/extents.c:4481
 ext4_map_blocks+0x23a/0xff0 fs/ext4/inode.c:623
 ext4_alloc_file_blocks+0x1e6/0x6e0 fs/ext4/extents.c:4670
 ext4_fallocate+0x57a/0x1460 fs/ext4/extents.c:4955
 vfs_fallocate+0x3be/0x650 fs/open.c:309
 ioctl_preallocate+0x12b/0x190 fs/ioctl.c:491
 file_ioctl fs/ioctl.c:537 [inline]
 do_vfs_ioctl+0xb14/0xcf0 fs/ioctl.c:732
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:754
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff85c7d0d0 of 8 bytes by task 10 on cpu 0:
 rcu_gp_fqs_loop+0x23c/0x580 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x143/0x230 kernel/rcu/tree.c:1821
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10 Comm: rcu_preempt Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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