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BUG: KCSAN: data-race in __percpu_counter_compare / percpu_counter_add_batch

write to 0xffff888100049310 of 8 bytes by task 20480 on cpu 1:
 percpu_counter_add_batch+0x9c/0xd0 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 mm/shmem.c:1582 [inline]
 shmem_getpage_gfp+0x8eb/0x1410 mm/shmem.c:1895
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_write_begin+0x7e/0x100 mm/shmem.c:2530
 generic_perform_write+0x196/0x3a0 mm/filemap.c:3582
 __generic_file_write_iter+0x161/0x300 mm/filemap.c:3711
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3743
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888100049310 of 8 bytes by task 20479 on cpu 0:
 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 mm/shmem.c:1582 [inline]
 shmem_getpage_gfp+0x87a/0x1410 mm/shmem.c:1895
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_write_begin+0x7e/0x100 mm/shmem.c:2530
 generic_perform_write+0x196/0x3a0 mm/filemap.c:3582
 __generic_file_write_iter+0x161/0x300 mm/filemap.c:3711
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3743
 call_write_iter include/linux/fs.h:1977 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20479 Comm: syz-executor.3 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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