linux-kernel - Re: [PATCH 1/1] arm/stacktrace: stop unwinding after an invalid address.

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Date:   Wed, 15 Nov 2017 11:26:34 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     "mingo@...nel.org" <mingo@...nel.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        PANKAJ MISHRA <pankaj.m@...sung.com>,
        AMIT SAHRAWAT <a.sahrawat@...sung.com>,
        Vaneet Narang <v.narang@...sung.com>
Subject: Re: [PATCH 1/1] arm/stacktrace: stop unwinding after an invalid
 address.

On Wed, Nov 15, 2017 at 11:09:22AM +0000, Maninder Singh wrote:
> Hi Russell,
> 
> >On Tue, Oct 24, 2017 at 05:16:42PM +0530, Maninder Singh wrote:
> >> This patch stops unwinding backtrace in case of below 2 cases.
> >> 
> >> (Issue observed while porting stackdepot on ARM, duplicate
> >> entries created in stackdepot
> >> reference patch for workaround in stackdepot:-
> >> https://lkml.org/lkml/2017/10/11/353
> >> ).
> >> 
> >> 1. If address belongs to irq/exception code, ignore it.
> >> save_stack+0x40/0xec
> >>  __set_page_owner+0x2c/0x64
> >> ....
> >> ....
> >>  __handle_domain_irq+0x9c/0x130
> >>  gic_handle_irq+0x40/0x80
> >>  __irq_usr+0x4c/0x60
> >>  0xb6507818
> >> ^^^^^^^
> >
> >However, we _do_ want to trace through an IRQ taken in SVC mode, but you
> >completely remove all that code.  So, not taking this patch, sorry.
> 
> OK. Thanks.
> 
> But can we add some marker to distinguish before and after interrupt context frames.
> so that we can remove interrupt that frames from stackdepot, because due to interrupt allocations,
> we end up with so many stackdepot entries and which results in more memory consumption by stackdepot.

Notice that I said "taken in SVC mode" not "taken in user mode".  Your
example below is for a user mode interrupt.

> Something like below:
> __set_page_owner+0x2c/0x64
> ...
> ...
> __handle_domain_irq+0x9c/0x130
> gic_handle_irq+0x40/0x80
> __irq_usr+0x4c/0x60
> 0xFFFFFFFF (marker)
> 0xb6507818
> ....
> 
> 
> Thus in stackdepot we can save before 0xFFFFFFF.
> or can you provide any suggestion for the same if we can try for?

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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