Am 18.03.2015 um 23:29 schrieb Andy Lutomirski: > On Wed, Mar 18, 2015 at 3:22 PM, Jiri Kosina <jkos...@suse.cz> wrote: >> On Wed, 18 Mar 2015, Andy Lutomirski wrote: >> >>> sysret64 can only fail with #GP, and we're totally screwed if that >>> happens, >> >> But what if the GPF handler pagefaults afterwards? It'd be operating on >> user stack already. > > Good point. > > Stefan, can you try changing the first "jne > opportunistic_sysret_failed" to "jmp opportunistic_sysret_failed" in > entry_64.S and seeing if you can reproduce this? (Is it easy enough > to reproduce that this would tell us anything?)
I have no good way of reproducing the issue (happens once per week...) but apparently Takashi has, so I'd like to hand this task over to him. > It's a shame that double_fault doesn't record what gs was on entry. > If we did sysret -> general_protection -> page_fault -> double_fault, > then we'd enter double_fault with usergs, whereas syscall -> > page_fault -> double_fault would enter double_fault with kernelgs. > > Hmm. We may be able to answer this more directly. Stefan, can you > dump a couple hundred bytes starting at 0x00007fffa55eafb8 (i.e. your > page_fault stack at the time of the failure)? That will tell us the > faulting address. If that fails, try starting at 00007fffa55eb000 > instead. Unfortunately not, is this userspace memory? It's not in the dump I have. This issue is the first I have seen where having a full dump would be really helpful apart from cosmetic reasons... -- Stefan Seyfried Linux Consultant & Developer -- GPG Key: 0x731B665B B1 Systems GmbH Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
