[PATCHv2 1/2] powerpc/pseries: group lmb operation and memblock's

[PATCHv2 1/2] powerpc/pseries: group lmb operation and memblock's

[Pingfan Liu]

This patch prepares for the incoming patch which swaps the order of KOBJ_
uevent and dt's updating.

It has no functional effect, just groups lmb operation and memblock's in
order to insert dt updating operation easily, and makes it easier to
review.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Leonardo Bras <leonardo@linux.ibm.com>
Cc: Libor Pechacek <lpechacek@suse.cz>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: kexec@lists.infradead.org
---
 arch/powerpc/platforms/pseries/hotplug-memory.c | 26 ++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index b2cde17..4bd9004 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -377,7 +377,8 @@ static int dlpar_add_lmb(struct drmem_lmb *);
 static int dlpar_remove_lmb(struct drmem_lmb *lmb)
 {
 	unsigned long block_sz;
-	int rc;
+	phys_addr_t base_addr;
+	int rc, nid;
 
 	if (!lmb_is_removable(lmb))
 		return -EINVAL;
@@ -386,17 +387,19 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
 	if (rc)
 		return rc;
 
+	base_addr = lmb->base_addr;
+	nid = lmb->nid;
 	block_sz = pseries_memory_block_size();
 
-	__remove_memory(lmb->nid, lmb->base_addr, block_sz);
-
-	/* Update memory regions for memory remove */
-	memblock_remove(lmb->base_addr, block_sz);
-
 	invalidate_lmb_associativity_index(lmb);
 	lmb_clear_nid(lmb);
 	lmb->flags &= ~DRCONF_MEM_ASSIGNED;
 
+	__remove_memory(nid, base_addr, block_sz);
+
+	/* Update memory regions for memory remove */
+	memblock_remove(base_addr, block_sz);
+
 	return 0;
 }
 
@@ -663,6 +666,8 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
 	}
 
 	lmb_set_nid(lmb);
+	lmb->flags |= DRCONF_MEM_ASSIGNED;
+
 	block_sz = memory_block_size_bytes();
 
 	/* Add the memory */
@@ -674,11 +679,14 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
 
 	rc = dlpar_online_lmb(lmb);
 	if (rc) {
-		__remove_memory(lmb->nid, lmb->base_addr, block_sz);
+		int nid = lmb->nid;
+		phys_addr_t base_addr = lmb->base_addr;
+
 		invalidate_lmb_associativity_index(lmb);
 		lmb_clear_nid(lmb);
-	} else {
-		lmb->flags |= DRCONF_MEM_ASSIGNED;
+		lmb->flags &= ~DRCONF_MEM_ASSIGNED;
+
+		__remove_memory(nid, base_addr, block_sz);
 	}
 
 	return rc;
-- 
2.7.5

[PATCHv2 2/2] powerpc/pseries: update device tree before ejecting hotplug uevents

[Pingfan Liu]

A bug is observed on pseries by taking the following steps on rhel:
-1. drmgr -c mem -r -q 5
-2. echo c > /proc/sysrq-trigger

And then, the failure looks like:
kdump: saving to /sysroot//var/crash/127.0.0.1-2020-01-16-02:06:14/
kdump: saving vmcore-dmesg.txt
kdump: saving vmcore-dmesg.txt complete
kdump: saving vmcore
 Checking for memory holes                         : [  0.0 %] /                   Checking for memory holes                         : [100.0 %] |                   Excluding unnecessary pages                       : [100.0 %] \                   Copying data                                      : [  0.3 %] -          eta: 38s[   44.337636] hash-mmu: mm: Hashing failure ! EA=0x7fffba400000 access=0x8000000000000004 current=makedumpfile
[   44.337663] hash-mmu:     trap=0x300 vsid=0x13a109c ssize=1 base psize=2 psize 2 pte=0xc000000050000504
[   44.337677] hash-mmu: mm: Hashing failure ! EA=0x7fffba400000 access=0x8000000000000004 current=makedumpfile
[   44.337692] hash-mmu:     trap=0x300 vsid=0x13a109c ssize=1 base psize=2 psize 2 pte=0xc000000050000504
[   44.337708] makedumpfile[469]: unhandled signal 7 at 00007fffba400000 nip 00007fffbbc4d7fc lr 000000011356ca3c code 2
[   44.338548] Core dump to |/bin/false pipe failed
/lib/kdump-lib-initramfs.sh: line 98:   469 Bus error               $CORE_COLLECTOR /proc/vmcore $_mp/$KDUMP_PATH/$HOST_IP-$DATEDIR/vmcore-incomplete
kdump: saving vmcore failed

* Root cause *
  After analyzing, it turns out that in the current implementation,
when hot-removing lmb, the KOBJ_REMOVE event ejects before the dt updating as
the code __remove_memory() comes before drmem_update_dt().
So in kdump kernel, when read_from_oldmem() resorts to
pSeries_lpar_hpte_insert() to install hpte, but fails with -2 due to
non-exist pfn. And finally, low_hash_fault() raise SIGBUS to process, as it
can be observed "Bus error"

From a viewpoint of listener and publisher, the publisher notifies the
listener before data is ready.  This introduces a problem where udev
launches kexec-tools (due to KOBJ_REMOVE) and loads a stale dt before
updating. And in capture kernel, makedumpfile will access the memory based
on the stale dt info, and hit a SIGBUS error due to an un-existed lmb.

* Fix *
  In order to fix this issue, update dt before __remove_memory(), and
accordingly the same rule in hot-add path.

This will introduce extra dt updating payload for each involved lmb when hotplug.
But it should be fine since drmem_update_dt() is memory based operation and
hotplug is not a hot path.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Leonardo Bras <leonardo@linux.ibm.com> 
Cc: Libor Pechacek <lpechacek@suse.cz> 
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com> 
To: linuxppc-dev@lists.ozlabs.org
Cc: kexec@lists.infradead.org
---
v1 -> v2: improve commit, and more detail about the SIGBUG failure path
 arch/powerpc/platforms/pseries/hotplug-memory.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 4bd9004..72cd4a5 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -394,6 +394,9 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
 	invalidate_lmb_associativity_index(lmb);
 	lmb_clear_nid(lmb);
 	lmb->flags &= ~DRCONF_MEM_ASSIGNED;
+	rtas_hp_event = true;
+	drmem_update_dt();
+	rtas_hp_event = false;
 
 	__remove_memory(nid, base_addr, block_sz);
 
@@ -667,6 +670,9 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
 
 	lmb_set_nid(lmb);
 	lmb->flags |= DRCONF_MEM_ASSIGNED;
+	rtas_hp_event = true;
+	drmem_update_dt();
+	rtas_hp_event = false;
 
 	block_sz = memory_block_size_bytes();
 
@@ -685,6 +691,9 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
 		invalidate_lmb_associativity_index(lmb);
 		lmb_clear_nid(lmb);
 		lmb->flags &= ~DRCONF_MEM_ASSIGNED;
+		rtas_hp_event = true;
+		drmem_update_dt();
+		rtas_hp_event = false;
 
 		__remove_memory(nid, base_addr, block_sz);
 	}
@@ -941,12 +950,6 @@ int dlpar_memory(struct pseries_hp_errorlog *hp_elog)
 		break;
 	}
 
-	if (!rc) {
-		rtas_hp_event = true;
-		rc = drmem_update_dt();
-		rtas_hp_event = false;
-	}
-
 	unlock_device_hotplug();
 	return rc;
 }
-- 
2.7.5