[syzbot] BUG: using smp_processor_id() in preemptible code in __do_user_fault

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a74e6a01 Merge tag 's390-5.12-3' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14f67ae6d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c7ac5ce2d1160e16
dashboard link: https://syzkaller.appspot.com/bug?extid=a7ee43e564223f195c84
userspace arch: arm

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a7ee43...@syzkaller.appspotmail.com

BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor.0/15841
caller is debug_smp_processor_id+0x20/0x24 lib/smp_processor_id.c:64
CPU: 0 PID: 15841 Comm: syz-executor.0 Not tainted 5.12.0-rc2-syzkaller #0
Hardware name: ARM-Versatile Express
Backtrace:
[<82107738>] (dump_backtrace) from [<821079ac>] (show_stack+0x18/0x1c arch/arm/kernel/traps.c:252)
r7:00000000 r6:60000113 r5:00000000 r4:83966184
[<82107994>] (show_stack) from [<82110980>] (__dump_stack lib/dump_stack.c:79 [inline])
[<82107994>] (show_stack) from [<82110980>] (dump_stack+0xb8/0xe8 lib/dump_stack.c:120)
[<821108c8>] (dump_stack) from [<82133120>] (check_preemption_disabled+0x118/0x11c lib/smp_processor_id.c:53)
r7:8294d26c r6:00000000 r5:82133144 r4:86d725b0
[<82133008>] (check_preemption_disabled) from [<82133144>] (debug_smp_processor_id+0x20/0x24 lib/smp_processor_id.c:64)
r7:00000a07 r6:86d72080 r5:0000000b r4:ffffc000
[<82133124>] (debug_smp_processor_id) from [<80217a00>] (harden_branch_predictor arch/arm/include/asm/system_misc.h:24 [inline])
[<82133124>] (debug_smp_processor_id) from [<80217a00>] (__do_user_fault+0x98/0x108 arch/arm/mm/fault.c:142)
[<80217968>] (__do_user_fault) from [<80217c90>] (do_page_fault+0x190/0x378 arch/arm/mm/fault.c:357)
r9:00000800 r8:84649ebc r7:84649e40 r6:00000a07 r5:ffffc000 r4:89063fb0
[<80217b00>] (do_page_fault) from [<80218054>] (do_DataAbort+0x38/0xb8 arch/arm/mm/fault.c:522)
r10:7ef2f914 r9:76f276d0 r8:80217b00 r7:89063fb0 r6:ffffc000 r5:00000a07
r4:83837b38
[<8021801c>] (do_DataAbort) from [<80200dc4>] (__dabt_usr+0x44/0x60 arch/arm/kernel/entry-armv.S:421)
Exception stack(0x89063fb0 to 0x89063ff8)
3fa0: ffffff00 20000280 ffffc000 20000250
3fc0: 00000004 20070517 00000140 20ffb000 7ef2f79a 76f276d0 7ef2f914 76f2720c
3fe0: 00000000 76f27020 00000006 00013b18 80000010 ffffffff
r8:30c5387d r7:30c5387d r6:ffffffff r5:80000010 r4:00013b18


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[Tetsuo Handa]

Something like
https://lkml.kernel.org/r/fa786d1c-db06-f7f1...@I-love.SAKURA.ne.jp
is expected.

For now workarounded on syzkaller side.
https://github.com/google/syzkaller/commit/88250aee0f2ad81f49ea13da4410ceae261e3cfa

#syz invalid