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

[Mahesh J Salgaonkar]

From: Mahesh Salgaonkar <mahesh at 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]
[  325.384338]   NIP: [00007fffaae585f4] PID: 7168 Comm: find
[  325.384339]   Initiator: CPU
[  325.384341]   Error type: UE [Load/Store]
[  325.384343]     Effective address: 00007fffaafe28ac
[  325.384345]     Physical address:  00002017c0bd0000
[  325.384350] find[7168]: unhandled signal 7 at 00007fffaae585f4 nip 00007fffaae585f4 lr 00007fffaae585e0 code 4
[  325.388574] 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")
Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
---
 arch/powerpc/kernel/mce_power.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
index fe6fc63251fe..63b58ae5d601 100644
--- a/arch/powerpc/kernel/mce_power.c
+++ b/arch/powerpc/kernel/mce_power.c
@@ -441,7 +441,6 @@ static int mce_handle_ierror(struct pt_regs *regs,
 					if (pfn != ULONG_MAX) {
 						*phys_addr =
 							(pfn << PAGE_SHIFT);
-						handled = 1;
 					}
 				}
 			}
@@ -532,9 +531,8 @@ 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;
 	}
@@ -572,7 +570,7 @@ 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;