Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack | Date | Wed, 10 Jun 2020 21:38:56 +0200 |
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Qian Cai <cai@lca.pw> writes: > On Tue, Jun 09, 2020 at 10:50:50PM +0200, Thomas Gleixner wrote: >> Thomas Gleixner <tglx@linutronix.de> writes: >> >> BAD (after oom02) >> >> # cat /sys/kernel/debug/stackdepot/info >> >> Unique stacks: 140476 >> > >> > That's indeed odd. I try to reproduce and figure out what really breaks >> > here. >> >> I checked your config file and I think I know where this comes from. Can >> you plase disable KASAN just for testing purposes and compare before >> after again? > > It turns out I'll need a few days to be able to get ahold of those > affected systems again. I'll be reporting back as soon as possible.
I figured it out. It has nothing to do with asm_call_on...(). It's also unrelated to page_owner. It's purely a KASAN issue.
KASAN trims stack traces with the help of filter_irq_stacks() which relies on __irqentry_text_start/end
The entry rework moved the interrupt entry points out of the irqentry section, which breaks that filter function.
I made it work again. Here are the numbers which make that obvious:
Mainline: Unique stacks: 23403 Depot index: 244 Depot offset: 4208
x86/entry: Unique stacks: 38835 Depot index: 464 Depot offset: 7616
x86/entry + fix: Unique stacks: 23607 Depot index: 247 Depot offset: 14224
So with the non-working trimming this generates more unique stacks and because they are not trimmed they become larger and eat more storage space. The resulting average per stack shows that:
Mainline: 171 bytes per stack x86/entry: 195 bytes per stack x86/entry + fix: 172 bytes per stack
I'll point you to a test branch shortly.
Thanks,
tglx
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