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

Pingfan Liu
2020-08-27T06:36:35Z

Hello guys. Do you have further comments on this version?

Thanks,
Pingfan

On Mon, Aug 10, 2020 at 4:53 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> 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