Messages in this thread | | | Date | Thu, 24 Jul 2014 20:59:38 +0200 | From | Peter Zijlstra <> | Subject | Re: Random panic in load_balance() with 3.16-rc |
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On Thu, Jul 24, 2014 at 11:47:17AM -0700, Linus Torvalds wrote: > However, that constant spilling part just counts as "too stupid to > live". The real bug is this: > > movq $load_balance_mask, -136(%rbp) #, %sfp > subq $184, %rsp #, > > where gcc creates the stack frame *after* having already used it to > save that constant *deep* below the stack frame. > > The x86-64 ABI specifies a 128-byte red-zone under the stack pointer, > and this is ok by that limit. It looks like it's illegal (136 > 128), > but the fact is, we've had four "pushq"s to update %rsp since loading > the frame pointer, so it's just *barely* legal with the red-zoning. > > But we build the kernel with -mno-red-zone. We do *not* follow the > x86-64 ABI wrt redzoning, because we *cannot*: interrupts while in > kernel mode *will* use the stack without a redzone. So that > "-mno-red-zone" is not some "optional guideline". It's a hard and > harsh requirement for the kernel, and gcc-4.9 is a buggy piece of shit > for ignoring it. And your bug happens becuase you happen to hit an > interrupt _just_ in that single instruction window (or perhaps hit > some other similar case and corrupted kernel data structures earlier).
Ooh, shiny, I so missed all that (also didn't know about red-zones etc..).
Glad this got sorted.
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