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BUG: KCSAN: data-race in rcu_gp_fqs_loop / rcu_preempt_deferred_qs_irqrestore

read to 0xffffffff85c7d0d0 of 8 bytes by task 10 on cpu 1:
 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

write to 0xffffffff85c7d0d0 of 8 bytes by task 25723 on cpu 0:
 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]
 __find_get_block_slow fs/buffer.c:210 [inline]
 __find_get_block fs/buffer.c:1336 [inline]
 __find_get_block+0x394/0x760 fs/buffer.c:1330
 __getblk_gfp+0x50/0x570 fs/buffer.c:1358
 sb_getblk include/linux/buffer_head.h:325 [inline]
 ext4_getblk+0x10b/0x380 fs/ext4/inode.c:834
 ext4_bread+0x4a/0x210 fs/ext4/inode.c:877
 __ext4_read_dirblock+0x3e/0x700 fs/ext4/namei.c:112
 ext4_add_entry+0x478/0x8f0 fs/ext4/namei.c:2214
 ext4_add_nondir+0x61/0x190 fs/ext4/namei.c:2561
 ext4_symlink+0x629/0x9b0 fs/ext4/namei.c:3344
 vfs_symlink fs/namei.c:4131 [inline]
 vfs_symlink+0x218/0x310 fs/namei.c:4117
 do_symlinkat+0x1a5/0x1e0 fs/namei.c:4158
 __do_sys_symlink fs/namei.c:4177 [inline]
 __se_sys_symlink fs/namei.c:4175 [inline]
 __x64_sys_symlink+0x3f/0x50 fs/namei.c:4175
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25723 Comm: syz-executor.3 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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