Re: linux v5.18.3 fails to boot

[John David Anglin <dave.anglin@bell.net>]

On 2022-06-10 12:06 p.m., Kuniyuki Iwashima wrote:
> Hello,
> Thanks for heads up!
>
> Date:   Fri, 10 Jun 2022 11:06:24 -0400
> From:   John David Anglin <dave.anglin@bell.net>
>> I did a regression search. e039c0b5985999b150594126225e1ee51df7b4c9 is the first bad commit
>>
>> commit e039c0b5985999b150594126225e1ee51df7b4c9
>> Author: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
>> Date:   Fri Apr 29 14:38:01 2022 -0700
>>
>>       list: fix a data-race around ep->rdllist
>>
>>       [ Upstream commit d679ae94fdd5d3ab00c35078f5af5f37e068b03d ]
>>
>>       ep_poll() first calls ep_events_available() with no lock held and checks
>>       if ep->rdllist is empty by list_empty_careful(), which reads
>>       rdllist->prev.  Thus all accesses to it need some protection to avoid
>>       store/load-tearing.
>>
>>       Note INIT_LIST_HEAD_RCU() already has the annotation for both prev
>>       and next.
>>
>>       Commit bf3b9f6372c4 ("epoll: Add busy poll support to epoll with socket
>>       fds.") added the first lockless ep_events_available(), and commit
>>       c5a282e9635e ("fs/epoll: reduce the scope of wq lock in epoll_wait()")
>>       made some ep_events_available() calls lockless and added single call under
>>       a lock, finally commit e59d3c64cba6 ("epoll: eliminate unnecessary lock
>>       for zero timeout") made the last ep_events_available() lockless.
>>
>>       BUG: KCSAN: data-race in do_epoll_wait / do_epoll_wait
>>
>>       write to 0xffff88810480c7d8 of 8 bytes by task 1802 on cpu 0:
>>        INIT_LIST_HEAD include/linux/list.h:38 [inline]
>>        list_splice_init include/linux/list.h:492 [inline]
>>        ep_start_scan fs/eventpoll.c:622 [inline]
>>        ep_send_events fs/eventpoll.c:1656 [inline]
>>        ep_poll fs/eventpoll.c:1806 [inline]
>>        do_epoll_wait+0x4eb/0xf40 fs/eventpoll.c:2234
>>        do_epoll_pwait fs/eventpoll.c:2268 [inline]
>>        __do_sys_epoll_pwait fs/eventpoll.c:2281 [inline]
>>        __se_sys_epoll_pwait+0x12b/0x240 fs/eventpoll.c:2275
>>        __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2275
>>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>        do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
>>        entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>>       read to 0xffff88810480c7d8 of 8 bytes by task 1799 on cpu 1:
>>        list_empty_careful include/linux/list.h:329 [inline]
>>        ep_events_available fs/eventpoll.c:381 [inline]
>>        ep_poll fs/eventpoll.c:1797 [inline]
>>        do_epoll_wait+0x279/0xf40 fs/eventpoll.c:2234
>>        do_epoll_pwait fs/eventpoll.c:2268 [inline]
>>        __do_sys_epoll_pwait fs/eventpoll.c:2281 [inline]
>>        __se_sys_epoll_pwait+0x12b/0x240 fs/eventpoll.c:2275
>>        __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2275
>>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>        do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
>>        entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>>       value changed: 0xffff88810480c7d0 -> 0xffff888103c15098
>>
>>       Reported by Kernel Concurrency Sanitizer on:
>>       CPU: 1 PID: 1799 Comm: syz-fuzzer Tainted: G        W 5.17.0-rc7-syzkaller-dirty #0
>>       Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>
>>       Link: https://lkml.kernel.org/r/20220322002653.33865-3-kuniyu@amazon.co.jp
>>       Fixes: e59d3c64cba6 ("epoll: eliminate unnecessary lock for zero timeout")
>>       Fixes: c5a282e9635e ("fs/epoll: reduce the scope of wq lock in epoll_wait()")
>>       Fixes: bf3b9f6372c4 ("epoll: Add busy poll support to epoll with socket fds.")
>>       Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
>>       Reported-by: syzbot+bdd6e38a1ed5ee58d8bd@syzkaller.appspotmail.com
>>       Cc: Al Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org>
>>       Cc: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
>>       Cc: Kuniyuki Iwashima <kuni1840@gmail.com>
>>       Cc: "Soheil Hassas Yeganeh" <soheil@google.com>
>>       Cc: Davidlohr Bueso <dave@stgolabs.net>
>>       Cc: "Sridhar Samudrala" <sridhar.samudrala@intel.com>
>>       Cc: Alexander Duyck <alexander.h.duyck@intel.com>
>>       Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>>       Signed-off-by: Sasha Levin <sashal@kernel.org>
>>
>>    include/linux/list.h | 6 +++---
>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> Reverting above change fixes v5.18.3 boot.
>>
>> It seems the most significant byte of the "ldd -10(r3),rp" instruction in mpt_reply has been
>> set to 0:
>>
>>       4084:       bf 80 21 18     cmpb,*<> r0,ret0,4118 <mpt_reply+0x1b8>
>>       4088:       08 04 02 5b     copy r4,dp
>>       408c:       00 00 04 00     sync
>>       4090:       0c 61 10 c2     ldd -10(r3),rp
>>
>> See IIR value in crash output.
> The commit was added to prevent compiler optimisation from splitting
> read/write operations.  I think it can lead in a change in opcodes but
> must be safe.  So I'm not sure why the commit causes boot failure for now.
Neither am I.
>
> I'm not familiar with PARISC and this may be a stupid question though,
> what does `ldd` exactly do? and which line is it executed in the func/file?
ldd performs a 64-bit load to register rp (r2).  It is part of mpt_reply's epilogue.
The prior "sync" instruction corresponds to the "mb()" at the end of mpt_reply.

I would have thought this code should have been write protected.  It seems
CONFIG_STRICT_MODULE_RWX is not explicitly set in config:

CONFIG_ARCH_HAS_STRICT_KERNEL_RWX=y
CONFIG_STRICT_KERNEL_RWX=y

I think I need to try enabling CONFIG_STRICT_MODULE_RWX.

>
>
>> On 2022-06-09 2:13 p.m., John David Anglin wrote:
>>> [...]
>>> ata3: SATA link down (SStatus 0 SControl 0)
>>>        _______________________________
>>>       < Your System ate a SPARC! Gah! >
>>>        -------------------------------
>>>               \   ^__^
>>>                   (__)\       )\/\
>>>                    U  ||----w |
>>>                       ||     ||
>>> swapper/0 (pid 0): Illegal instruction (code 8)
>>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.18.3+ #1
>>> Hardware name: 9000/785/C8000
>>>
>>>       YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI
>>> PSW: 00001000000001000001101100001110 Not tainted
>>> r00-03  0000000008041b0e 000000004e8045b0 0000000010bbda78 000000004e804470
>>> r04-07  0000000010bb5000 0000000000001440 0000000054355000 0000000000001400
>>> r08-11  0000000055000000 000000000000000e 000000000000000f 0000000055002800
>>> r12-15  0000000000000000 0000000055002800 0000000040b668c0 0000000040b668c0
>>> r16-19  0000000000000001 0000000000000001 0000000051b799f0 0000000000000000
>>> r20-23  0000000000000001 fffffffffffff5b9 0000000000000000 0000000000200000
>>> r24-27  000000000000000c 000000000800000e 0000000054355144 0000000040b3e0c0
>>> r28-31  0000000000010001 000000004e804620 000000004e8045b0 0000000040edd040
>>> sr00-03  00000000000a5c00 0000000000000000 0000000000000000 00000000000a5c00
>>> sr04-07  0000000000000000 0000000000000000 0000000000000000 0000000000000000
>>>
>>> IASQ: 0000000000000000 0000000000000000 IAOQ: 0000000010bbd9e0 0000000010bbd9e4
>>>   IIR: 006110c2    ISR: 0000000010240000  IOR: 00000003b76dd048
>>>   CPU:        0   CR30: 0000000040edd040 CR31: ffffffffffffffff
>>>   ORIG_R28: 0000000000000000
>>>   IAOQ[0]: mpt_reply+0x130/0x4f0 [mptbase]
>>>   IAOQ[1]: mpt_reply+0x134/0x4f0 [mptbase]
>>>   RP(r2): mpt_reply+0x1c8/0x4f0 [mptbase]
>>> Backtrace:
>>>   [<0000000010bbde24>] mpt_interrupt+0x84/0xe8 [mptbase]
>>>   [<000000004026dd64>] __handle_irq_event_percpu+0xc4/0x250
>>>   [<000000004026df28>] handle_irq_event_percpu+0x38/0xd8
>>>   [<00000000402776c4>] handle_percpu_irq+0xb4/0xf0
>>>   [<000000004026c90c>] generic_handle_irq+0x5c/0x90
>>>   [<00000000401a20e4>] call_on_stack+0x18/0x24
>>>
>>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.18.3+ #1
>>> Hardware name: 9000/785/C8000
>>> Backtrace:
>>>   [<00000000401a8cd8>] show_stack+0x70/0x90
>>>   [<0000000040a8e238>] dump_stack_lvl+0xd8/0x128
>>>   [<0000000040a8e2bc>] dump_stack+0x34/0x48
>>>   [<00000000401a8efc>] die_if_kernel+0x1e4/0x3f8
>>>   [<00000000401a9af4>] handle_interruption+0x59c/0xb58
>>>   [<00000000401a107c>] intr_check_sig+0x0/0x3c
> Can you decode these stacktraces with ./scripts/decode_stacktrace.sh ?
I don't think this is helpful as the code in mpt_reply has been corrupted.
>
>
>>> Kernel panic - not syncing: Fatal exception in interrupt
>>>
>>> v5.18.2 with similar config is okay.  The fault seems consistent. IIR contains illegal instruction.
>>>
>>> Attached config.
> Also, can you forward this config to me?
>
> Best regards,
> Kuniyuki


-- 
John David Anglin  dave.anglin@bell.net