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@xxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx> Cc: Nathan Lynch <nathanl@xxxxxxxxxxxxx> To: linuxppc-dev@xxxxxxxxxxxxxxxx Cc: kexec@xxxxxxxxxxxxxxxxxxx --- v2 -> v3: rebase onto ppc next-test branch --- arch/powerpc/platforms/pseries/hotplug-memory.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c index 1a3ac3b..def8cb3f 100644 --- a/arch/powerpc/platforms/pseries/hotplug-memory.c +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c @@ -372,6 +372,7 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb) invalidate_lmb_associativity_index(lmb); lmb_clear_nid(lmb); lmb->flags &= ~DRCONF_MEM_ASSIGNED; + drmem_update_dt(); __remove_memory(nid, base_addr, block_sz); @@ -607,6 +608,7 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb) lmb_set_nid(lmb); lmb->flags |= DRCONF_MEM_ASSIGNED; + drmem_update_dt(); block_sz = memory_block_size_bytes(); @@ -625,6 +627,7 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb) invalidate_lmb_associativity_index(lmb); lmb_clear_nid(lmb); lmb->flags &= ~DRCONF_MEM_ASSIGNED; + drmem_update_dt(); __remove_memory(nid, base_addr, block_sz); } @@ -877,9 +880,6 @@ int dlpar_memory(struct pseries_hp_errorlog *hp_elog) break; } - if (!rc) - rc = drmem_update_dt(); - unlock_device_hotplug(); return rc; } -- 2.7.5 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
