[PATCHv5 2/2] powerpc/pseries: update device tree before ejecting hotplug uevents

Pingfan Liu
2020-08-10T08:53:30Z

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 *
This bug is introduced by commit 063b8b1251fd
("powerpc/pseries/memory-hotplug: Only update DT once per memory DLPAR
request"), which tried to combine all the dt updating into one.

To fix this issue, meanwhile not to introduce a quadratic runtime
complexity by the model:
dlpar_memory_add_by_count
for_each_drmem_lmb <--
dlpar_add_lmb
drmem_update_dt(_v1|_v2)
for_each_drmem_lmb <--
The dt should still be only updated once, and just before the last memory
online/offline event is ejected to user space. Achieve this by tracing the
num of lmb added or removed.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: kexec@lists.infradead.org
---
v4 -> v5: change dlpar_add_lmb()/dlpar_remove_lmb() prototype to report
whether dt is updated successfully.
Fix a condition boundary check bug
v3 -> v4: resolve a quadratic runtime complexity issue.
This series is applied on next-test branch
arch/powerpc/platforms/pseries/hotplug-memory.c | 102 +++++++++++++++++++-----
1 file changed, 80 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 46cbcd1..1567d9f 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -350,13 +350,22 @@ static bool lmb_is_removable(struct drmem_lmb *lmb)
return true;
}

-static int dlpar_add_lmb(struct drmem_lmb *);
+enum dt_update_status {
+ DT_NOUPDATE,
+ DT_TOUPDATE,
+ DT_UPDATED,
+};
+
+/* "*dt_update" returns DT_UPDATED if updated */
+static int dlpar_add_lmb(struct drmem_lmb *lmb,
+ enum dt_update_status *dt_update);

-static int dlpar_remove_lmb(struct drmem_lmb *lmb)
+static int dlpar_remove_lmb(struct drmem_lmb *lmb,
+ enum dt_update_status *dt_update)
{
unsigned long block_sz;
phys_addr_t base_addr;
- int rc, nid;
+ int rc, ret, nid;

if (!lmb_is_removable(lmb))
return -EINVAL;
@@ -372,6 +381,13 @@ static int dlpar_remove_lmb(struct drmem_lmb *lmb)
invalidate_lmb_associativity_index(lmb);
lmb_clear_nid(lmb);
lmb->flags &= ~DRCONF_MEM_ASSIGNED;
+ if (*dt_update) {
+ ret = drmem_update_dt();
+ if (ret)
+ pr_warn("%s fail to update dt, but continue\n", __func__);
+ else
+ *dt_update = DT_UPDATED;
+ }

__remove_memory(nid, base_addr, block_sz);

@@ -387,6 +403,7 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
int lmbs_removed = 0;
int lmbs_available = 0;
int rc;
+ enum dt_update_status dt_update = DT_NOUPDATE;

pr_info("Attempting to hot-remove %d LMB(s)\n", lmbs_to_remove);

@@ -409,7 +426,11 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
}

for_each_drmem_lmb(lmb) {
- rc = dlpar_remove_lmb(lmb);
+
+ /* combine dt updating for all LMBs */
+ if (lmbs_to_remove - lmbs_removed <= 1)
+ dt_update = DT_TOUPDATE;
+ rc = dlpar_remove_lmb(lmb, &dt_update);
if (rc)
continue;

@@ -424,13 +445,17 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
}

if (lmbs_removed != lmbs_to_remove) {
+ enum dt_update_status rollback_dt_update = DT_NOUPDATE;
+
pr_err("Memory hot-remove failed, adding LMB's back\n");

for_each_drmem_lmb(lmb) {
if (!drmem_lmb_reserved(lmb))
continue;

- rc = dlpar_add_lmb(lmb);
+ if (--lmbs_removed == 0 && dt_update == DT_UPDATED)
+ rollback_dt_update = DT_TOUPDATE;
+ rc = dlpar_add_lmb(lmb, &rollback_dt_update);
if (rc)
pr_err("Failed to add LMB back, drc index %x\n",
lmb->drc_index);
@@ -458,6 +483,7 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)

static int dlpar_memory_remove_by_index(u32 drc_index)
{
+ enum dt_update_status dt_update = DT_TOUPDATE;
struct drmem_lmb *lmb;
int lmb_found;
int rc;
@@ -468,7 +494,7 @@ static int dlpar_memory_remove_by_index(u32 drc_index)
for_each_drmem_lmb(lmb) {
if (lmb->drc_index == drc_index) {
lmb_found = 1;
- rc = dlpar_remove_lmb(lmb);
+ rc = dlpar_remove_lmb(lmb, &dt_update);
if (!rc)
dlpar_release_drc(lmb->drc_index);

@@ -490,6 +516,7 @@ static int dlpar_memory_remove_by_index(u32 drc_index)

static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
{
+ enum dt_update_status dt_update = DT_NOUPDATE;
struct drmem_lmb *lmb, *start_lmb, *end_lmb;
int lmbs_available = 0;
int rc;
@@ -519,7 +546,9 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
if (!(lmb->flags & DRCONF_MEM_ASSIGNED))
continue;

- rc = dlpar_remove_lmb(lmb);
+ if (lmb == end_lmb)
+ dt_update = DT_TOUPDATE;
+ rc = dlpar_remove_lmb(lmb, &dt_update);
if (rc)
break;

@@ -527,14 +556,16 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
}

if (rc) {
- pr_err("Memory indexed-count-remove failed, adding any removed LMBs\n");
+ enum dt_update_status rollback_dt_update = DT_NOUPDATE;

+ pr_err("Memory indexed-count-remove failed, adding any removed LMBs\n");

for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) {
if (!drmem_lmb_reserved(lmb))
continue;
-
- rc = dlpar_add_lmb(lmb);
+ if (lmb == end_lmb && dt_update == DT_UPDATED)
+ rollback_dt_update = DT_TOUPDATE;
+ rc = dlpar_add_lmb(lmb, &rollback_dt_update);
if (rc)
pr_err("Failed to add LMB, drc index %x\n",
lmb->drc_index);
@@ -572,7 +603,7 @@ static inline int dlpar_memory_remove(struct pseries_hp_errorlog *hp_elog)
{
return -EOPNOTSUPP;
}
-static int dlpar_remove_lmb(struct drmem_lmb *lmb)
+static int dlpar_remove_lmb(struct drmem_lmb *lmb, bool dt_update)
{
return -EOPNOTSUPP;
}
@@ -591,10 +622,11 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
}
#endif /* CONFIG_MEMORY_HOTREMOVE */

-static int dlpar_add_lmb(struct drmem_lmb *lmb)
+static int dlpar_add_lmb(struct drmem_lmb *lmb,
+ enum dt_update_status *dt_update)
{
unsigned long block_sz;
- int rc;
+ int rc, ret;

if (lmb->flags & DRCONF_MEM_ASSIGNED)
return -EINVAL;
@@ -607,6 +639,13 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)

lmb_set_nid(lmb);
lmb->flags |= DRCONF_MEM_ASSIGNED;
+ if (*dt_update) {
+ ret = drmem_update_dt();
+ if (ret)
+ pr_warn("%s fail to update dt, but continue\n", __func__);
+ else
+ *dt_update = DT_UPDATED;
+ }

block_sz = memory_block_size_bytes();

@@ -616,6 +655,8 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
invalidate_lmb_associativity_index(lmb);
lmb_clear_nid(lmb);
lmb->flags &= ~DRCONF_MEM_ASSIGNED;
+ if (*dt_update == DT_UPDATED)
+ drmem_update_dt();
return rc;
}

@@ -627,7 +668,11 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
invalidate_lmb_associativity_index(lmb);
lmb_clear_nid(lmb);
lmb->flags &= ~DRCONF_MEM_ASSIGNED;
-
+ if (*dt_update == DT_UPDATED) {
+ ret = drmem_update_dt();
+ if (ret)
+ pr_warn("%s fail to update dt during rollback, but continue\n", __func__);
+ }
__remove_memory(nid, base_addr, block_sz);
}

@@ -636,6 +681,7 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)

static int dlpar_memory_add_by_count(u32 lmbs_to_add)
{
+ enum dt_update_status dt_update = DT_NOUPDATE;
struct drmem_lmb *lmb;
int lmbs_available = 0;
int lmbs_added = 0;
@@ -666,7 +712,9 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add)
if (rc)
continue;

- rc = dlpar_add_lmb(lmb);
+ if (lmbs_to_add - lmbs_added <= 1)
+ dt_update = DT_TOUPDATE;
+ rc = dlpar_add_lmb(lmb, &dt_update);
if (rc) {
dlpar_release_drc(lmb->drc_index);
continue;
@@ -683,13 +731,18 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add)
}

if (lmbs_added != lmbs_to_add) {
+ enum dt_update_status rollback_dt_update = DT_NOUPDATE;
+
pr_err("Memory hot-add failed, removing any added LMBs\n");

for_each_drmem_lmb(lmb) {
if (!drmem_lmb_reserved(lmb))
continue;

- rc = dlpar_remove_lmb(lmb);
+ if (--lmbs_added == 0 && dt_update == DT_UPDATED)
+ rollback_dt_update = DT_TOUPDATE;
+
+ rc = dlpar_remove_lmb(lmb, &rollback_dt_update);
if (rc)
pr_err("Failed to remove LMB, drc index %x\n",
lmb->drc_index);
@@ -716,6 +769,7 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add)

static int dlpar_memory_add_by_index(u32 drc_index)
{
+ enum dt_update_status dt_update = DT_TOUPDATE;
struct drmem_lmb *lmb;
int rc, lmb_found;

@@ -727,7 +781,7 @@ static int dlpar_memory_add_by_index(u32 drc_index)
lmb_found = 1;
rc = dlpar_acquire_drc(lmb->drc_index);
if (!rc) {
- rc = dlpar_add_lmb(lmb);
+ rc = dlpar_add_lmb(lmb, &dt_update);
if (rc)
dlpar_release_drc(lmb->drc_index);
}
@@ -750,6 +804,7 @@ static int dlpar_memory_add_by_index(u32 drc_index)

static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index)
{
+ enum dt_update_status dt_update = DT_NOUPDATE;
struct drmem_lmb *lmb, *start_lmb, *end_lmb;
int lmbs_available = 0;
int rc;
@@ -783,7 +838,9 @@ static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index)
if (rc)
break;

- rc = dlpar_add_lmb(lmb);
+ if (lmb == end_lmb)
+ dt_update = DT_TOUPDATE;
+ rc = dlpar_add_lmb(lmb, &dt_update);
if (rc) {
dlpar_release_drc(lmb->drc_index);
break;
@@ -796,10 +853,14 @@ static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index)
pr_err("Memory indexed-count-add failed, removing any added LMBs\n");

for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) {
+ enum dt_update_status rollback_dt_update = DT_NOUPDATE;
+
if (!drmem_lmb_reserved(lmb))
continue;

- rc = dlpar_remove_lmb(lmb);
+ if (lmb == end_lmb && dt_update == DT_UPDATED)
+ rollback_dt_update = DT_TOUPDATE;
+ rc = dlpar_remove_lmb(lmb, &rollback_dt_update);
if (rc)
pr_err("Failed to remove LMB, drc index %x\n",
lmb->drc_index);
@@ -879,9 +940,6 @@ int dlpar_memory(struct pseries_hp_errorlog *hp_elog)
break;
}

- if (!rc)
- rc = drmem_update_dt();
-
unlock_device_hotplug();
return rc;
}
--
2.7.5