[syzbot] [bpf?] KMSAN: uninit-value in percpu_array_map_lookup_percpu_elem

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    39cd87c4eb2b Linux 6.9-rc2
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13891cc5180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5112b3f484393436
dashboard link: https://syzkaller.appspot.com/bug?extid=aca389a8a7da35c070ce
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11629a19180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=169e86e5180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dba7eac545d2/disk-39cd87c4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ddf1c8e07b17/vmlinux-39cd87c4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/808527761eab/bzImage-39cd87c4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aca389a8a7da35c070ce@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in percpu_array_map_lookup_percpu_elem+0x1cb/0x200 kernel/bpf/arraymap.c:257
 percpu_array_map_lookup_percpu_elem+0x1cb/0x200 kernel/bpf/arraymap.c:257
 ____bpf_map_lookup_percpu_elem kernel/bpf/helpers.c:133 [inline]
 bpf_map_lookup_percpu_elem+0x67/0x90 kernel/bpf/helpers.c:130
 ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
 __bpf_prog_run288+0xb5/0xe0 kernel/bpf/core.c:2237
 bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
 __bpf_prog_run include/linux/filter.h:657 [inline]
 bpf_prog_run include/linux/filter.h:664 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
 bpf_trace_run8+0x1bd/0x3a0 kernel/trace/bpf_trace.c:2426
 __bpf_trace_jbd2_handle_stats+0x51/0x70 include/trace/events/jbd2.h:210
 trace_jbd2_handle_stats include/trace/events/jbd2.h:210 [inline]
 jbd2_journal_stop+0x1157/0x12c0 fs/jbd2/transaction.c:1869
 __ext4_journal_stop+0x115/0x310 fs/ext4/ext4_jbd2.c:134
 ext4_do_writepages+0x1c3c/0x62e0 fs/ext4/inode.c:2692
 ext4_writepages+0x312/0x830 fs/ext4/inode.c:2768
 do_writepages+0x427/0xc30 mm/page-writeback.c:2612
 __writeback_single_inode+0x10d/0x12c0 fs/fs-writeback.c:1650
 writeback_sb_inodes+0xb48/0x1be0 fs/fs-writeback.c:1941
 __writeback_inodes_wb+0x14c/0x440 fs/fs-writeback.c:2012
 wb_writeback+0x4da/0xdf0 fs/fs-writeback.c:2119
 wb_check_old_data_flush fs/fs-writeback.c:2223 [inline]
 wb_do_writeback fs/fs-writeback.c:2276 [inline]
 wb_workfn+0x110c/0x1940 fs/fs-writeback.c:2304
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0xa81/0x1bd0 kernel/workqueue.c:3335
 worker_thread+0xea5/0x1560 kernel/workqueue.c:3416
 kthread+0x3e2/0x540 kernel/kthread.c:388
 ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

Local variable stack created at:
 __bpf_prog_run288+0x45/0xe0 kernel/bpf/core.c:2237
 bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
 __bpf_prog_run include/linux/filter.h:657 [inline]
 bpf_prog_run include/linux/filter.h:664 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
 bpf_trace_run8+0x1bd/0x3a0 kernel/trace/bpf_trace.c:2426

CPU: 1 PID: 1070 Comm: kworker/u8:7 Not tainted 6.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: writeback wb_workfn (flush-8:0)
=====================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup