Messages in this thread | | | From | Arnd Bergmann <> | Date | Wed, 21 Oct 2020 13:58:21 +0200 | Subject | Re: [PATCH 0/3] IRQ stack support for ARM |
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(replying to my own mail, apparently my normal outgoing email server is blacklisted, so resending from @kernel.org)
On Fri, Oct 16, 2020 at 12:09 PM Arnd Bergmann <arnd@arndb.de> wrote: > > On Thu, Oct 8, 2020 at 10:32 AM Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > > On Thu, Oct 08, 2020 at 12:45:30PM +0530, Maninder Singh wrote: > > > Observed Stack Overflow on 8KB kernel stack on ARM specially > > > incase on network interrupts, which results in undeterministic behaviour. > > > So there is need for per cpu dedicated IRQ stack for ARM. > > > > > > As ARm does not have extra co-processor register > > > to save thread info pointer, IRQ stack will be at some > > > performance cost, so code is under CONFIG_IRQ_STACK. > > > > > > and we don't have much knowledge and set up for CLANG > > > and ARM_UNWIND, so dependency added for both cases. > > > > > > Tested patch set with QEMU for latest kernel > > > and 4.1 kernel for ARM target with same patch set. > > > > You need to investigate and show where and why this is happening. My > > guess is you have a network driver that uses a lot of kernel stack > > space, which itself would be a bug. > > Agreed. > > > Note that there are compiler versions out there that mis-optimise and > > eat stack space - the kernel build should be warning if a function > > uses a large amount of stack. > > Some more ideas for figuring it out: > > CONFIG_DEBUG_STACK_USAGE may also be helpful in identifying > code paths that are deeply nested with multiple functions taking a > lot of stack space, but each one staying under the limit. > > CONFIG_DEBUG_STACKOVERFLOW would also help here but > is not supported on Arm at the moment. There was a patch[1] from > Uwe Kleine-König to add this, and I suppose we should still add > that, in particular if it helps debug this problem. > > CONFIG_VMAP_STACK is probably the best way to debug > random runtime stack overflows because using a guard page > turns random memory corruption into an immediate oops, > but I don't think there is an implementation for Arm yet and > using a lot of vmalloc space means we might not be able to > default to this. > > Regardless of identifying and fixing the bug Maninder found, I > also think that supporting separate async stacks on Arm is useful > for determinism. Most of the popular architectures use irqstack > for this reason, and I was actually surprised that we don't do it > on arch/arm/. > > Arnd > > [1] https://lore.kernel.org/linux-arm-kernel/20200108082913.29710-1-u.kleine-koenig@pengutronix.de/
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