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=0x7fffba40
access=0x8004 current=makedumpfile
[ 44.337663] hash-mmu: trap=0x300 vsid=0x13a109c ssize=1 base psize=2
psize 2 pte=0xc0005504
[ 44.337677] hash-mmu: mm: Hashing failure ! EA=0x7fffba40
access=0x8004 current=makedumpfile
[ 44.337692] hash-mmu: trap=0x300 vsid=0x13a109c ssize=1 base psize=2
psize 2 pte=0xc0005504
[ 44.337708] makedumpfile[469]: unhandled signal 7 at 7fffba40 nip
7fffbbc4d7fc lr 00011356ca3c 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().
>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
Cc: Michael Ellerman
Cc: Benjamin Herrenschmidt
Cc: Paul Mackerras
Cc: Hari Bathini
To: linuxppc-dev@lists.ozlabs.org
Cc: ke...@lists.infradead.org
---
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 a3a9353..1f623c3 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -392,6 +392,9 @@ 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);
@@ -665,6 +668,9 @@ 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();
@@ -683,6 +689,9 @@ 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);
}
@@ -939,12 +948,6 @@ 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
