On Wed, Mar 18, 2015 at 3:40 PM, Andy Lutomirski <[email protected]> wrote: > On Wed, Mar 18, 2015 at 3:38 PM, Stefan Seyfried > <[email protected]> wrote: >> Am 18.03.2015 um 23:29 schrieb Andy Lutomirski: >>> On Wed, Mar 18, 2015 at 3:22 PM, Jiri Kosina <[email protected]> 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... > > Yes, it's userspace. Thanks for checking, though.
One more stupid hunch: Can you do: x/21xg ffff8801013d4f58 If I counted right, that'll dump task_pt_regs(current). --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
