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BUG: KCSAN: data-race in get_task_mm / page_cache_ra_unbounded

write to 0xffff888100bdd02c of 4 bytes by task 1 on cpu 1:
 memalloc_nofs_restore include/linux/sched/mm.h:258 [inline]
 page_cache_ra_unbounded+0x48c/0x4c0 mm/readahead.c:239
 ondemand_readahead+0x560/0x780 mm/readahead.c:267
 page_cache_sync_ra+0x18f/0x1a0 mm/readahead.c:577
 page_cache_sync_readahead include/linux/pagemap.h:840 [inline]
 filemap_get_pages+0x1ba/0x660 mm/filemap.c:2375
 filemap_read+0x1ba/0x7b0 mm/filemap.c:2458
 generic_file_read_iter+0x82/0x410 mm/filemap.c:2609
 ext4_file_read_iter+0x2e0/0x420 fs/ext4/file.c:74
 __kernel_read+0x306/0x580 fs/read_write.c:454
 integrity_kernel_read+0x4c/0x70 security/integrity/iint.c:191
 ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:484 [inline]
 ima_calc_file_shash security/integrity/ima/ima_crypto.c:515 [inline]
 ima_calc_file_hash+0x929/0x1310 security/integrity/ima/ima_crypto.c:572
 ima_collect_measurement+0x168/0x310 security/integrity/ima/ima_api.c:252
 process_measurement+0xa88/0x10f0 security/integrity/ima/ima_main.c:330
 ima_file_check+0x75/0xa0 security/integrity/ima/ima_main.c:499
 do_open fs/namei.c:3367 [inline]
 path_openat+0x19c5/0x21b0 fs/namei.c:3498
 do_filp_open+0xbd/0x1d0 fs/namei.c:3525
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_open fs/open.c:1211 [inline]
 __se_sys_open fs/open.c:1207 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1207
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888100bdd02c of 4 bytes by task 4833 on cpu 0:
 get_task_mm+0x3e/0x90 kernel/fork.c:1212
 get_task_cmdline fs/proc/base.c:347 [inline]
 proc_pid_cmdline_read+0x87/0x650 fs/proc/base.c:367
 vfs_read+0x154/0x5d0 fs/read_write.c:494
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4833 Comm: systemd-journal Not tainted 5.12.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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