On Mon, 2018-04-23 at 23:01 +1000, Nicholas Piggin wrote: > On Mon, 23 Apr 2018 21:14:12 +1000 > Balbir Singh <bsinghar...@gmail.com> wrote: > > > On Mon, Apr 23, 2018 at 8:33 PM, Mahesh Jagannath Salgaonkar > > <mah...@linux.vnet.ibm.com> wrote: > > > On 04/23/2018 12:21 PM, Balbir Singh wrote: > > > > On Mon, Apr 23, 2018 at 2:59 PM, Mahesh J Salgaonkar > > > > <mah...@linux.vnet.ibm.com> wrote: > > > > > From: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com> > > > > > > > > > > The current code extracts the physical address for UE errors and then > > > > > hooks it up into memory failure infrastructure. On successful > > > > > extraction > > > > > of physical address it wrongly sets "handled = 1" which means this UE > > > > > error > > > > > has been recovered. Since MCE handler gets return value as handled = > > > > > 1, it > > > > > assumes that error has been recovered and goes back to same NIP. This > > > > > causes > > > > > MCE interrupt again and again in a loop leading to hard lockup. > > > > > > > > > > Also, initialize phys_addr to ULONG_MAX so that we don't end up > > > > > queuing > > > > > undesired page to hwpoison. > > > > > > > > > > Without this patch we see: > > > > > [ 1476.541984] Severe Machine check interrupt [Recovered] > > > > > [ 1476.541985] NIP: [000000001002588c] PID: 7109 Comm: find > > > > > [ 1476.541986] Initiator: CPU > > > > > [ 1476.541987] Error type: UE [Load/Store] > > > > > [ 1476.541988] Effective address: 00007fffd2755940 > > > > > [ 1476.541989] Physical address: 000020181a080000 > > > > > [...] > > > > > [ 1476.542003] Severe Machine check interrupt [Recovered] > > > > > [ 1476.542004] NIP: [000000001002588c] PID: 7109 Comm: find > > > > > [ 1476.542005] Initiator: CPU > > > > > [ 1476.542006] Error type: UE [Load/Store] > > > > > [ 1476.542006] Effective address: 00007fffd2755940 > > > > > [ 1476.542007] Physical address: 000020181a080000 > > > > > [ 1476.542010] Severe Machine check interrupt [Recovered] > > > > > [ 1476.542012] NIP: [000000001002588c] PID: 7109 Comm: find > > > > > [ 1476.542013] Initiator: CPU > > > > > [ 1476.542014] Error type: UE [Load/Store] > > > > > [ 1476.542015] Effective address: 00007fffd2755940 > > > > > [ 1476.542016] Physical address: 000020181a080000 > > > > > [ 1476.542448] Memory failure: 0x20181a08: recovery action for dirty > > > > > LRU page: Recovered > > > > > [ 1476.542452] Memory failure: 0x20181a08: already hardware poisoned > > > > > [ 1476.542453] Memory failure: 0x20181a08: already hardware poisoned > > > > > [ 1476.542454] Memory failure: 0x20181a08: already hardware poisoned > > > > > [ 1476.542455] Memory failure: 0x20181a08: already hardware poisoned > > > > > [ 1476.542456] Memory failure: 0x20181a08: already hardware poisoned > > > > > [ 1476.542457] Memory failure: 0x20181a08: already hardware poisoned > > > > > [...] > > > > > [ 1490.972174] Watchdog CPU:38 Hard LOCKUP > > > > > > > > > > After this patch we see: > > > > > > > > > > [ 325.384336] Severe Machine check interrupt [Not recovered] > > > > > > > > How did you test for this? > > > > > > By injecting cache SUE using L2 FIR register (0x1001080c). > > > > > > > If the error was recovered, shouldn't the > > > > process have gotten > > > > a SIGBUS and we should have prevented further access as a part of the > > > > handling > > > > (memory_failure()). Do we just need a MF_MUST_KILL in the flags? > > > > > > We hook it up to memory_failure() through a work queue and by the time > > > work queue kicks in, the application continues to restart and hit same > > > NIP again and again. Every MCE again hooks the same address to memory > > > failure work queue and throws multiple recovered MCE messages for same > > > address. Once the memory_failure() hwpoisons the page, application gets > > > SIGBUS and then we are fine. > > > > > > > That seems quite broken and not recovered is very confusing. So effectively > > we can never recover from a MCE UE. I think we need a notion of delayed > > recovery then? Where we do recover, but mark is as recovered with delays? > > We might want to revisit our recovery process and see if the recovery > > requires > > to turn the MMU on, but that is for later, I suppose. > > The notion of being handled in the machine check return value is not > whether the failing resource is later de-allocated or fixed, but if > *this* particular exception was able to be corrected / processing > resume as normal without further action. > > The MCE UE is not recovered just by finding its address here, so I think > Mahesh's patch is right. >
OK, It would nice to see a "recovered" in the output as opposed to process killed, but the MCE is "not recovered"? The kernel bits do sound sane Balbir Singh.
