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BUG: KCSAN: data-race in __percpu_counter_compare / percpu_counter_add_batch

write to 0xffff88821b66a310 of 8 bytes by task 24392 on cpu 0:
 percpu_counter_add_batch+0xbd/0x130 lib/percpu_counter.c:91
 percpu_counter_add include/linux/percpu_counter.h:56 [inline]
 shmem_inode_acct_block mm/shmem.c:228 [inline]
 shmem_alloc_and_acct_page+0x1a5/0x650 mm/shmem.c:1582
 shmem_getpage_gfp+0x669/0x19c0 mm/shmem.c:1884
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_write_begin+0x83/0x100 mm/shmem.c:2521
 generic_perform_write+0x196/0x390 mm/filemap.c:3403
 __generic_file_write_iter+0x154/0x330 mm/filemap.c:3532
 generic_file_write_iter+0x2f3/0x3e0 mm/filemap.c:3564
 call_write_iter include/linux/fs.h:1882 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x665/0x6f0 fs/read_write.c:578
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821b66a310 of 8 bytes by task 24387 on cpu 1:
 percpu_counter_read include/linux/percpu_counter.h:72 [inline]
 __percpu_counter_compare+0x28/0x1c0 lib/percpu_counter.c:225
 percpu_counter_compare include/linux/percpu_counter.h:51 [inline]
 shmem_inode_acct_block mm/shmem.c:225 [inline]
 shmem_alloc_and_acct_page+0x12c/0x650 mm/shmem.c:1582
 shmem_getpage_gfp+0x669/0x19c0 mm/shmem.c:1884
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_write_begin+0x83/0x100 mm/shmem.c:2521
 generic_perform_write+0x196/0x390 mm/filemap.c:3403
 __generic_file_write_iter+0x154/0x330 mm/filemap.c:3532
 generic_file_write_iter+0x2f3/0x3e0 mm/filemap.c:3564
 call_write_iter include/linux/fs.h:1882 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x665/0x6f0 fs/read_write.c:578
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24387 Comm: syz-executor.4 Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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