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From:   Guo Ren <guoren@kernel.org>
Date:   Mon, 3 Jul 2023 11:09:59 +0800
Message-ID: <CAJF2gTR6u90hc-jDq3rq+m_kg4dcgE0TmTZA3tZ+StZQJkUCqg@mail.gmail.com>
Subject: Re: [PATCH -next V17 4/7] riscv: entry: Convert to generic entry
To:     Daniel Thompson <daniel.thompson@linaro.org>
Cc:     arnd@arndb.de, palmer@rivosinc.com, tglx@linutronix.de,
        peterz@infradead.org, luto@kernel.org, conor.dooley@microchip.com,
        heiko@sntech.de, jszhang@kernel.org, lazyparser@gmail.com,
        falcon@tinylab.org, chenhuacai@kernel.org, apatel@ventanamicro.com,
        atishp@atishpatra.org, mark.rutland@arm.com, ben@decadent.org.uk,
        bjorn@kernel.org, palmer@dabbelt.com, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        Guo Ren <guoren@linux.alibaba.com>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>,
        Yipeng Zou <zouyipeng@huawei.com>,
        Vincent Chen <vincent.chen@sifive.com>
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On Sat, Jul 1, 2023 at 12:22=E2=80=AFPM Guo Ren <guoren@kernel.org> wrote:
>
> On Sat, Jul 1, 2023 at 11:08=E2=80=AFAM Guo Ren <guoren@kernel.org> wrote=
:
> >
> > On Sat, Jul 1, 2023 at 10:55=E2=80=AFAM Guo Ren <guoren@kernel.org> wro=
te:
> > >
> > > On Fri, Jun 30, 2023 at 10:51=E2=80=AFPM Daniel Thompson
> > > <daniel.thompson@linaro.org> wrote:
> > > >
> > > > On Fri, Jun 30, 2023 at 07:22:40AM -0400, Guo Ren wrote:
> > > > > On Fri, Jun 30, 2023 at 7:16=E2=80=AFAM Guo Ren <guoren@kernel.or=
g> wrote:
> > > > > >
> > > > > > On Thu, Jun 29, 2023 at 10:02=E2=80=AFAM Daniel Thompson
> > > > > > <daniel.thompson@linaro.org> wrote:
> > > > > > >
> > > > > > > On Tue, Feb 21, 2023 at 10:30:18PM -0500, guoren@kernel.org w=
rote:
> > > > > > > > From: Guo Ren <guoren@linux.alibaba.com>
> > > > > > > >
> > > > > > > > This patch converts riscv to use the generic entry infrastr=
ucture from
> > > > > > > > kernel/entry/*. The generic entry makes maintainers' work e=
asier and
> > > > > > > > codes more elegant. Here are the changes:
> > > > > > > >
> > > > > > > >  - More clear entry.S with handle_exception and ret_from_ex=
ception
> > > > > > > >  - Get rid of complex custom signal implementation
> > > > > > > >  - Move syscall procedure from assembly to C, which is much=
 more
> > > > > > > >    readable.
> > > > > > > >  - Connect ret_from_fork & ret_from_kernel_thread to generi=
c entry.
> > > > > > > >  - Wrap with irqentry_enter/exit and syscall_enter/exit_fro=
m_user_mode
> > > > > > > >  - Use the standard preemption code instead of custom
> > > > > > > >
> > > > > > > > Suggested-by: Huacai Chen <chenhuacai@kernel.org>
> > > > > > > > Reviewed-by: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>
> > > > > > > > Tested-by: Yipeng Zou <zouyipeng@huawei.com>
> > > > > > > > Tested-by: Jisheng Zhang <jszhang@kernel.org>
> > > > > > > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > > > > > > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > > > > > > Cc: Ben Hutchings <ben@decadent.org.uk>
> > > > > > >
> > > > > > > Apologies for the late feedback but I've been swamped lately =
and only
> > > > > > > recently got round to running the full kgdb test suite on the=
 v6.4
> > > > > > > series.
> > > > > > >
> > > > > > > The kgdb test suite includes a couple of tests that verify th=
at the
> > > > > > > system resumes after breakpointing due to a BUG():
> > > > > > > https://github.com/daniel-thompson/kgdbtest/blob/master/tests=
/test_kdb_fault_injection.py#L24-L45
> > > > > > >
> > > > > > > These tests have regressed on riscv between v6.3 and v6.4 and=
 a bisect
> > > > > > > is pointing at this patch. With these changes in place then, =
after kdb
> > > > > > > resumes the system, the BUG() message is printed as normal bu=
t then
> > > > > > > immediately fails. From the backtrace it looks like the new e=
ntry/exit
> > > > > > > code cannot advance past a compiled breakpoint instruction:
> > > > > > > ~~~
> > > > > > > PANIC: Fatal exception in interrupt
> > > > > > It comes from:
> > > > > > void die(struct pt_regs *regs, ...
> > > > > > {
> > > > > > ...
> > > > > > if (in_interrupt())
> > > > > >         panic("Fatal exception in interrupt");
> > > > > > ...
> > > > > >
> > > > > > We could add a dump_backtrace to see what happened:
> > > > > > if (in_interrupt()) {
> > > > > > +      dump_backtrace(regs, NULL, KERN_DEFAULT);
> > > > > Sorry, it should be:
> > > > > +        dump_backtrace(NULL, NULL, KERN_DEFAULT);
> > > > > We need current stack info, not exception context.
> > > >
> > > > I added this... and I also stopped kgdb from intercepting the panic=
()
> > > > since that interferes with the console output from dump_backtrace()=
.
> > > >
> > > > ~~~
> > > > # /bin/echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
> > > > [    3.380565] lkdtm: Performing direct entry BUG
> > > >
> > > > Entering kdb (current=3D0xff6000000380ab00, pid 98) on processor 0 =
due to NonMaskable Interrupt @ 0xffffffff8064b844
> > > > kdb> go
> > > > Catastrophic error detected
> > > > kdb_continue_catastrophic=3D0, type go a second time if you really =
want to continue
> > > > kdb> go
> > > > Catastrophic error detected
> > > > kdb_continue_catastrophic=3D0, attempting to continue
> > > > [    3.381411] ------------[ cut here ]------------
> > > > [    3.381454] kernel BUG at drivers/misc/lkdtm/bugs.c:78!
> > > > [    3.381609] Kernel BUG [#1]
> > > > [    3.381632] Modules linked in:
> > > > [    3.381734] CPU: 0 PID: 98 Comm: echo Not tainted 6.4.0-rc6-0000=
4-ge6e9d4598760-dirty #126
> > > > [    3.381817] Hardware name: riscv-virtio,qemu (DT)
> > > > [    3.381885] epc : lkdtm_BUG+0x6/0x8
> > > > [    3.381959]  ra : lkdtm_do_action+0x10/0x1c
> > > > [    3.381978] epc : ffffffff8064b844 ra : ffffffff8064afb4 sp : ff=
200000008c3d30
> > > > [    3.381991]  gp : ffffffff810665a0 tp : ff6000000380ab00 t0 : 65=
00000000000000
> > > > [    3.382002]  t1 : 0000000000000001 t2 : 6550203a6d74646b s0 : ff=
200000008c3d40
> > > > [    3.382012]  s1 : ff60000003988000 a0 : ffffffff80fc0260 a1 : ff=
6000003ffad788
> > > > [    3.382023]  a2 : ff6000003ffb9530 a3 : 0000000000000000 a4 : 00=
00000000000000
> > > > [    3.382034]  a5 : ffffffff8064b83e a6 : 0000000000000050 a7 : 00=
00000000040000
> > > > [    3.382045]  s2 : 0000000000000004 s3 : ffffffff80fc0260 s4 : ff=
200000008c3e70
> > > > [    3.382056]  s5 : ff600000033223a8 s6 : 00000000000f0cc0 s7 : ff=
60000002211000
> > > > [    3.382066]  s8 : 00ffffffafc50c08 s9 : 00ffffffafc4b9b8 s10: 00=
00000000000000
> > > > [    3.382077]  s11: 0000000000000001 t3 : 461f715700000000 t4 : 00=
00000000000002
> > > > [    3.382087]  t5 : 0000000000000000 t6 : ff200000008c3b58
> > > > [    3.382097] status: 0000000200000120 badaddr: 0000000000000000 c=
ause: 0000000000000003
> > > > [    3.382139] [<ffffffff8064b844>] lkdtm_BUG+0x6/0x8
> > > > [    3.382245] Code: 0513 9245 b097 0039 80e7 7f20 bf39 1141 e422 0=
800 (9002) 1141
> > > > [    3.594697] ---[ end trace 0000000000000000 ]---
> > > >
> > > > At this point we expect a shell prompt since we should have taken t=
he BUG(),
> > > > killed the echo process and returned to the shell. However in v6.4 =
we get the
> > > > following instead (including the instrumentation you asked for):
> > >
> > > After comparing with arm64, I found that arm64 uses spinlock_irq to
> > > protect the in_interrupt(). I think this would make in_interrupt() =
=3D
> > > 0.
> > >
> > > So how about trying:
> > >
> > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > > index 5158961ea977..0ac914a99ee3 100644
> > > --- a/arch/riscv/kernel/traps.c
> > > +++ b/arch/riscv/kernel/traps.c
> > > @@ -82,13 +82,15 @@ void die(struct pt_regs *regs, const char *str)
> > >
> > >         bust_spinlocks(0);
> > >         add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
> > > -       spin_unlock_irqrestore(&die_lock, flags);
> > >         oops_exit();
> > >
> > >         if (in_interrupt())
> > >                 panic("Fatal exception in interrupt");
> > >         if (panic_on_oops)
> > >                 panic("Fatal exception");
> > > +
> > > +       spin_unlock_irqrestore(&die_lock, flags);
> > En... It seems it's not correct, how can I reproduce your environment
> > on qemu? Sorry, I'm not familiar with kgdb.
>
> I got it:
> Normal is:
> # mount -t debugfs none /sys/kernel/debug/
> # /bin/echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
> [    8.948041] lkdtm: Performing direct entry BUG
> [    8.949228] ------------[ cut here ]------------
> [    8.949640] kernel BUG at drivers/misc/lkdtm/bugs.c:78!
> [    8.950534] Kernel BUG [#1]
> [    8.950944] Modules linked in:
> [    8.951805] CPU: 0 PID: 106 Comm: echo Not tainted
> 6.3.0-rc2-00295-gb4e5219985e8 #22
> [    8.952831] Hardware name: riscv-virtio,qemu (DT)
> [    8.953587] epc : lkdtm_BUG+0x6/0x8
> [    8.954232]  ra : lkdtm_do_action+0x14/0x1c
> [    8.954713] epc : ffffffff805549e2 ra : ffffffff8087245c sp :
> ff2000000081bd60
> [    8.955378]  gp : ffffffff814ffec0 tp : ff600000023c8000 t0 :
> 6500000000000000
> [    8.956029]  t1 : 000000000000006c t2 : 6550203a6d74646b s0 :
> ff2000000081bd70
> [    8.956699]  s1 : ffffffff814bee50 a0 : ffffffff814bee50 a1 :
> ff6000001fbd8608
> [    8.957381]  a2 : ff6000001fbdb868 a3 : 0000000000000000 a4 :
> 0000000000000000
> [    8.958035]  a5 : ffffffff805549dc a6 : 0000000000000032 a7 :
> 0000000000000038
> [    8.958708]  s2 : 0000000000000004 s3 : 00000000556371a0 s4 :
> ff2000000081be90
> [    8.959397]  s5 : ff60000001c90000 s6 : 00000000556371a0 s7 :
> 0000000000000030
> [    8.960053]  s8 : 000000007fffec78 s9 : 0000000000000007 s10:
> 0000000055637480
> [    8.960717]  s11: 0000000000000001 t3 : ffffffff81512e97 t4 :
> ffffffff81512e97
> [    8.961379]  t5 : ffffffff81512e98 t6 : ff2000000081bba8
> [    8.961888] status: 0000000100000120 badaddr: 0000000000000000
> cause: 0000000000000003
> [    8.962923] [<ffffffff805549e2>] lkdtm_BUG+0x6/0x8
> [    8.964194] Code: 0513 d665 7097 0031 80e7 f000 b705 1141 e422 0800
> (9002) 1141
> [    8.965847] ---[ end trace 0000000000000000 ]---
> [    8.966637] note: echo[106] exited with irqs disabled
> Segmentation fault
> #
>
> After generic_entry:
> # mount -t debugfs none /sys/kernel/debug/
> # /bin/echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
> [    8.152247] lkdtm: Performing direct entry BUG
> [    8.153652] ------------[ cut here ]------------
> [    8.153825] kernel BUG at drivers/misc/lkdtm/bugs.c:78!
> [    8.154341] Kernel BUG [#1]
> [    8.154440] Modules linked in:
> [    8.154918] CPU: 0 PID: 106 Comm: echo Not tainted
> 6.4.0-rc1-00055-g0ca05a4b079f #21
> [    8.155301] Hardware name: riscv-virtio,qemu (DT)
> [    8.155581] epc : lkdtm_BUG+0x6/0x8
> [    8.155880]  ra : lkdtm_do_action+0x14/0x1c
> [    8.155977] epc : ffffffff8059d4b4 ra : ffffffff808c1a84 sp :
> ff2000000081bd40
> [    8.156030]  gp : ffffffff81503c08 tp : ff600000028ebac0 t0 :
> 6500000000000000
> [    8.156079]  t1 : 000000000000006c t2 : 6550203a6d74646b s0 :
> ff2000000081bd50
> [    8.156144]  s1 : ffffffff814c2e88 a0 : ffffffff814c2e88 a1 :
> ff6000001ffd8608
> [    8.156193]  a2 : ff6000001ffdb870 a3 : 0000000000000000 a4 :
> 0000000000000000
> [    8.156241]  a5 : ffffffff8059d4ae a6 : 0000000000000032 a7 :
> 0000000000000038
> [    8.156288]  s2 : 0000000000000004 s3 : 00000000556371a0 s4 :
> ff2000000081be70
> [    8.156335]  s5 : ff60000002090000 s6 : 00000000556371a0 s7 :
> 0000000000000030
> [    8.156382]  s8 : 000000007fffec78 s9 : 0000000000000007 s10:
> 0000000055637480
> [    8.156428]  s11: 0000000000000001 t3 : ffffffff815173d7 t4 :
> ffffffff815173d7
> [    8.156473]  t5 : ffffffff815173d8 t6 : ff2000000081bb88
> [    8.156516] status: 0000000100000120 badaddr: 0000000000000000
> cause: 0000000000000003
> [    8.156830] [<ffffffff8059d4b4>] lkdtm_BUG+0x6/0x8
> [    8.157630] Code: 0513 1745 d097 0031 80e7 70a0 b705 1141 e422 0800
> (9002) 1141
> [    8.169646] ---[ end trace 0000000000000000 ]---
> [    8.170148] Kernel panic - not syncing: Fatal exception in interrupt
> [    8.171839] ---[ end Kernel panic - not syncing: Fatal exception in
> interrupt ]---
>
> I'm debugging on it, and soon give the patch.
Thx, Daniel, for the report; here is the fixup:
https://lore.kernel.org/linux-riscv/20230702025708.784106-1-guoren@kernel.o=
rg/

I've tested, and it's okay now.
# /bin/echo BUG > /sys/kernel/debug/provoke-crash/DIRECT

>
> >
> > > +
> > >         if (ret !=3D NOTIFY_STOP)
> > >                 make_task_dead(SIGSEGV);
> > >  }
> > >
> > > >
> > > > [    3.594801] [<ffffffff80005e3a>] dump_backtrace+0x1c/0x24
> > > > [    3.594826] [<ffffffff800059f0>] die+0x228/0x238
> > > > [    3.594835] [<ffffffff80005b38>] handle_break+0x9a/0xe0
> > > > [    3.594843] [<ffffffff809f30d6>] do_trap_break+0x48/0x5c
> > > > [    3.594854] [<ffffffff80003ee4>] ret_from_exception+0x0/0x64
> > > > [    3.594862] [<ffffffff8064b844>] lkdtm_BUG+0x6/0x8
> > > > [    3.594959] Kernel panic - not syncing: Fatal exception in inter=
rupt
> > > > [    3.595005] SMP: stopping secondary CPUs
> > > > [    3.596444] ---[ end Kernel panic - not syncing: Fatal exception=
 in interrupt ]---
> > > > ~~~
> > > >
> > > >
> > > > Daniel.
> > >
> > >
> > >
> > > --
> > > Best Regards
> > >  Guo Ren
> >
> >
> >
> > --
> > Best Regards
> >  Guo Ren
>
>
>
> --
> Best Regards
>  Guo Ren


--=20
Best Regards
 Guo Ren