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BUG: KCSAN: data-race in __percpu_counter_compare / percpu_counter_add_batch

write to 0xffff88810004b3d0 of 8 bytes by task 7148 on cpu 0:
 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+0x8be/0x13d0 mm/shmem.c:1905
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_fallocate+0x544/0x840 mm/shmem.c:2739
 vfs_fallocate+0x463/0x660 fs/open.c:311
 file_ioctl fs/ioctl.c:497 [inline]
 do_vfs_ioctl+0x1322/0x1410 fs/ioctl.c:1048
 __do_sys_ioctl fs/ioctl.c:1067 [inline]
 __se_sys_ioctl+0x83/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810004b3d0 of 8 bytes by task 7142 on cpu 1:
 percpu_counter_read include/linux/percpu_counter.h:72 [inline]
 __percpu_counter_compare+0x28/0x1a0 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+0x84d/0x13d0 mm/shmem.c:1905
 shmem_getpage mm/shmem.c:155 [inline]
 shmem_fallocate+0x544/0x840 mm/shmem.c:2739
 vfs_fallocate+0x463/0x660 fs/open.c:311
 file_ioctl fs/ioctl.c:497 [inline]
 do_vfs_ioctl+0x1322/0x1410 fs/ioctl.c:1048
 __do_sys_ioctl fs/ioctl.c:1067 [inline]
 __se_sys_ioctl+0x83/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000000075af -> 0x00000000000075cf

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7142 Comm: syz-executor.0 Not tainted 5.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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