ACK: [SRU][Bionic][PATCH 1/1] powerpc/mce: Fix a bug where mce loops on memory UE.

[Stefan Bader]

On 05.06.2018 09:21, Joseph Salisbury wrote:
> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1774964
> 
> 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:
>   Severe Machine check interrupt [Recovered]
>     NIP: [000000001002588c] PID: 7109 Comm: find
>     Initiator: CPU
>     Error type: UE [Load/Store]
>       Effective address: 00007fffd2755940
>       Physical address:  000020181a080000
>   ...
>   Severe Machine check interrupt [Recovered]
>     NIP: [000000001002588c] PID: 7109 Comm: find
>     Initiator: CPU
>     Error type: UE [Load/Store]
>       Effective address: 00007fffd2755940
>       Physical address:  000020181a080000
>   Severe Machine check interrupt [Recovered]
>     NIP: [000000001002588c] PID: 7109 Comm: find
>     Initiator: CPU
>     Error type: UE [Load/Store]
>       Effective address: 00007fffd2755940
>       Physical address:  000020181a080000
>   Memory failure: 0x20181a08: recovery action for dirty LRU page: Recovered
>   Memory failure: 0x20181a08: already hardware poisoned
>   Memory failure: 0x20181a08: already hardware poisoned
>   Memory failure: 0x20181a08: already hardware poisoned
>   Memory failure: 0x20181a08: already hardware poisoned
>   Memory failure: 0x20181a08: already hardware poisoned
>   Memory failure: 0x20181a08: already hardware poisoned
>   ...
>   Watchdog CPU:38 Hard LOCKUP
> 
> After this patch we see:
> 
>   Severe Machine check interrupt [Not recovered]
>     NIP: [00007fffaae585f4] PID: 7168 Comm: find
>     Initiator: CPU
>     Error type: UE [Load/Store]
>       Effective address: 00007fffaafe28ac
>       Physical address:  00002017c0bd0000
>   find[7168]: unhandled signal 7 at 00007fffaae585f4 nip 00007fffaae585f4 lr 00007fffaae585e0 code 4
>   Memory failure: 0x2017c0bd: recovery action for dirty LRU page: Recovered
> 
> Fixes: 01eaac2b0591 ("powerpc/mce: Hookup ierror (instruction) UE errors")
> Fixes: ba41e1e1ccb9 ("powerpc/mce: Hookup derror (load/store) UE errors")
> Cc: stable at vger.kernel.org # v4.15+
> Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> Signed-off-by: Balbir Singh <bsingharora at gmail.com>
> Reviewed-by: Balbir Singh <bsingharora at gmail.com>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> (cherry picked from commit 75ecfb49516c53da00c57b9efe48fa3f5504a791)
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  arch/powerpc/kernel/mce_power.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
> index 644f704..aa15142 100644
> --- a/arch/powerpc/kernel/mce_power.c
> +++ b/arch/powerpc/kernel/mce_power.c
> @@ -552,7 +552,6 @@ static int mce_handle_ierror(struct pt_regs *regs,
>  					if (pfn != ULONG_MAX) {
>  						*phys_addr =
>  							(pfn << PAGE_SHIFT);
> -						handled = 1;
>  					}
>  				}
>  			}
> @@ -643,9 +642,7 @@ static int mce_handle_derror(struct pt_regs *regs,
>  			 * kernel/exception-64s.h
>  			 */
>  			if (get_paca()->in_mce < MAX_MCE_DEPTH)
> -				if (!mce_find_instr_ea_and_pfn(regs, addr,
> -								phys_addr))
> -					handled = 1;
> +				mce_find_instr_ea_and_pfn(regs, addr, phys_addr);
>  		}
>  		found = 1;
>  	}
> @@ -683,7 +680,7 @@ static long mce_handle_error(struct pt_regs *regs,
>  		const struct mce_ierror_table itable[])
>  {
>  	struct mce_error_info mce_err = { 0 };
> -	uint64_t addr, phys_addr;
> +	uint64_t addr, phys_addr = ULONG_MAX;
>  	uint64_t srr1 = regs->msr;
>  	long handled;
>  
> 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: OpenPGP digital signature
URL: <https://lists.ubuntu.com/archives/kernel-team/attachments/20180606/efb23eaf/attachment.sig>