From: Doug Anderson <dianders@chromium.org>
To: Sumit Garg <sumit.garg@linaro.org>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
Will Deacon <will@kernel.org>, Wei Li <liwei391@huawei.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Daniel Thompson <daniel.thompson@linaro.org>,
Jason Wessel <jason.wessel@windriver.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/2] arm64: kgdb/kdb: Fix pending single-step debugging issues
Date: Mon, 11 Apr 2022 17:09:07 -0700 [thread overview]
Message-ID: <CAD=FV=WZXBG98nKp4qq_=B+VmJ=MUAJJdOhaV4OkAT=AvDcTfg@mail.gmail.com> (raw)
In-Reply-To: <20220411093819.1012583-1-sumit.garg@linaro.org>
Hi,
On Mon, Apr 11, 2022 at 2:38 AM Sumit Garg <sumit.garg@linaro.org> wrote:
>
> This patch-set reworks pending fixes from Wei's series [1] to make
> single-step debugging via kgdb/kdb on arm64 work as expected. There was
> a prior discussion on ML [2] regarding if we should keep the interrupts
> enabled during single-stepping but it turns out that in case of kgdb, it
> is risky to enable interrupts as sometimes a resume after single
> stepping an interrupt handler leads to following unbalanced locking
> issue:
>
> [ 300.328300] WARNING: bad unlock balance detected!
> [ 300.328608] 5.18.0-rc1-00016-g3e732ebf7316-dirty #6 Not tainted
> [ 300.329058] -------------------------------------
> [ 300.329298] sh/173 is trying to release lock (dbg_slave_lock) at:
> [ 300.329718] [<ffffd57c951c016c>] kgdb_cpu_enter+0x7ac/0x820
> [ 300.330029] but there are no more locks to release!
> [ 300.330265]
> [ 300.330265] other info that might help us debug this:
> [ 300.330668] 4 locks held by sh/173:
> [ 300.330891] #0: ffff4f5e454d8438 (sb_writers#3){.+.+}-{0:0}, at: vfs_write+0x98/0x204
> [ 300.331735] #1: ffffd57c973bc2f0 (dbg_slave_lock){+.+.}-{2:2}, at: kgdb_cpu_enter+0x5b4/0x820
> [ 300.332259] #2: ffffd57c973a9460 (rcu_read_lock){....}-{1:2}, at: kgdb_cpu_enter+0xe0/0x820
> [ 300.332717] #3: ffffd57c973bc2a8 (dbg_master_lock){....}-{2:2}, at: kgdb_cpu_enter+0x1ec/0x820
>
> So, I choose to keep interrupts disabled specifically for kgdb. This
> series has been rebased to Linux 5.18-rc1 and I have dropped Doug's
> review and test tags as there is significant rework involved.
Hmmmm. I guess it's really up to Will here, but re-reading his
previous email made it pretty clear that he wasn't willing to land a
solution that he wasn't willing to land a solution that left
interrupts disabled during step. He also pointed out some things that
would actually be broken, like single-stepping over a call to
irqs_disabled() or single stepping over something that caused an
exception where the exception handler needed interrupts enabled.
I thought he had a proposal at:
https://lore.kernel.org/r/20200626095551.GA9312@willie-the-truck
...that was supposed to make all the problems go away and it was just
that nobody had time to implement his proposal?
> [1] https://lore.kernel.org/all/20200509214159.19680-1-liwei391@huawei.com/
> [2] https://lore.kernel.org/all/CAD=FV=Voyfq3Qz0T3RY+aYWYJ0utdH=P_AweB=13rcV8GDBeyQ@mail.gmail.com/
>
> Sumit Garg (2):
> arm64: kgdb: Fix incorrect single stepping into the irq handler
> arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step
>
> arch/arm64/include/asm/debug-monitors.h | 1 +
> arch/arm64/kernel/debug-monitors.c | 5 ++++
> arch/arm64/kernel/kgdb.c | 35 +++++++++++++++++++++++--
> 3 files changed, 39 insertions(+), 2 deletions(-)
>
> --
> 2.25.1
>
next prev parent reply other threads:[~2022-04-12 0:09 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-11 9:38 [PATCH 0/2] arm64: kgdb/kdb: Fix pending single-step debugging issues Sumit Garg
2022-04-11 9:38 ` [PATCH 1/2] arm64: kgdb: Fix incorrect single stepping into the irq handler Sumit Garg
2022-04-11 9:38 ` [PATCH 2/2] arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step Sumit Garg
2022-04-12 0:09 ` Doug Anderson [this message]
2022-04-13 7:03 ` [PATCH 0/2] arm64: kgdb/kdb: Fix pending single-step debugging issues Sumit Garg
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