Messages in this thread | | | Date | Thu, 07 Dec 2017 14:32:52 +0000 | From | James Morse <> | Subject | Re: [PATCH RESEND] arm64: fault: avoid send SIGBUS two times |
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Hi gengdongjiu, Will,
On 07/12/17 05:55, gengdongjiu wrote: > On 2017/12/7 0:15, Will Deacon wrote: >>> --- a/arch/arm64/mm/fault.c >>> +++ b/arch/arm64/mm/fault.c >>> @@ -570,7 +570,6 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) >>> { >>> struct siginfo info; >>> const struct fault_info *inf; >>> - int ret = 0; >>> >>> inf = esr_to_fault_info(esr); >>> pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n", >>> @@ -585,7 +584,7 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) >>> if (interrupts_enabled(regs)) >>> nmi_enter(); >>> >>> - ret = ghes_notify_sea(); >>> + ghes_notify_sea(); >>> >>> if (interrupts_enabled(regs)) >>> nmi_exit(); >>> @@ -600,7 +599,7 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) >>> info.si_addr = (void __user *)addr; >>> arm64_notify_die("", regs, &info, esr); >>> >>> - return ret; >>> + return 0;
>> Hmm, so this code is a bit of mess. >> >> Wouldn't it be better to have the signal dispatching code in do_mem_abort >> check ESR.ESR_ELx_FnV, so then do_sea wouldn't have to, and we could just >> return an error instead?
FnV only applies to one of the Synchronous External Abort ESRs, hence it ended up in here.
> Regardless ghes_notify_sea()'s return value, it always needs to deliver signal, > because ghes_notify_sea()'s return value does not reflect whether the memory error > handler(memory_failure()) handle the error successfully or failed. If let do_mem_abort() > delivers the signal, we should always let do_sea() return error, then the do_mem_abort() can > always deliver signal. Then we will see the strange log as shown below when happen Synchronous External Abort. > > [ 676.700652] Synchronous External Abort: synchronous external abort (0x96000410) at 0x0000000033ff7008 > [ 676.723301] Unhandled fault: synchronous external abort (0x96000410) at 0x0000000033ff7008 > > so I think it is better send the signal in the do_sea(), not send it in the do_mem_abort().
I agree: I think improving the commit message would help here, something like: --------- do_sea() calls arm64_notify_die() which will always signal user-space. It also returns whether APEI claimed the external abort as a RAS notification. If it returns failure do_mem_abort() will signal user-space too.
do_mem_abort() wants to know if we handled the error, we always call arm64_notify_die() so can always return success. ---------
APEI's return value matters for KVM, and it will matter here too if we support kernel-first.
> do_mem_abort() only send the signal when the exception does not defined in fault_info[]. Another benefit > is that do_sea() can send different signal according to the Synchronous External Abort type, such as SIGBUS or SIGKILL. > the do_mem_abort() can only send one kind signal.
(I'm not convinced we want to do this other than via the firwmare/kernel RAS code, but that is a separate issue)
Thanks,
James
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