[PATCH] powerpc/hotplug: assign hot added LMB to the right node

[PATCH] powerpc/hotplug: assign hot added LMB to the right node

[Laurent Dufour]

This patch applies to 5.9 and earlier kernels only.

Since 5.10, this has been fortunately fixed by the commit
e5e179aa3a39 ("pseries/drmem: don't cache node id in drmem_lmb struct").

When LMBs are added to a running system, the node id assigned to the LMB is
fetched from the temporary DT node provided by the hypervisor.

However, LMBs added are always assigned to the first online node. This is a
mistake and this is because hot_add_drconf_scn_to_nid() called by
lmb_set_nid() is checking for the LMB flags DRCONF_MEM_ASSIGNED which is
set later in dlpar_add_lmb().

To fix this issue, simply set that flag earlier in dlpar_add_lmb().

Note, this code has been rewrote in 5.10 and thus this fix has no meaning
since this version.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Scott Cheloha <cheloha@linux.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: stable@vger.kernel.org
---
 arch/powerpc/platforms/pseries/hotplug-memory.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index e54dcbd04b2f..92d83915c629 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -663,12 +663,14 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
 		return rc;
 	}
 
+	lmb->flags |= DRCONF_MEM_ASSIGNED;
 	lmb_set_nid(lmb);
 	block_sz = memory_block_size_bytes();
 
 	/* Add the memory */
 	rc = __add_memory(lmb->nid, lmb->base_addr, block_sz);
 	if (rc) {
+		lmb->flags &= ~DRCONF_MEM_ASSIGNED;
 		invalidate_lmb_associativity_index(lmb);
 		return rc;
 	}
@@ -676,10 +678,9 @@ 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);
+		lmb->flags &= ~DRCONF_MEM_ASSIGNED;
 		invalidate_lmb_associativity_index(lmb);
 		lmb_clear_nid(lmb);
-	} else {
-		lmb->flags |= DRCONF_MEM_ASSIGNED;
 	}
 
 	return rc;
-- 
2.29.2

Re: [PATCH] powerpc/hotplug: assign hot added LMB to the right node

[Greg KH]

On Thu, Dec 03, 2020 at 11:15:14AM +0100, Laurent Dufour wrote:
> This patch applies to 5.9 and earlier kernels only.
> 
> Since 5.10, this has been fortunately fixed by the commit
> e5e179aa3a39 ("pseries/drmem: don't cache node id in drmem_lmb struct").

Why can't we just backport that patch instead?  It's almost always
better to do that than to have a one-off patch, as almost always those
have bugs in them.

thanks,

greg k-h

Re: [PATCH] powerpc/hotplug: assign hot added LMB to the right node

[Laurent Dufour]

Le 03/12/2020 à 19:25, Greg KH a écrit :
> On Thu, Dec 03, 2020 at 11:15:14AM +0100, Laurent Dufour wrote:
>> This patch applies to 5.9 and earlier kernels only.
>>
>> Since 5.10, this has been fortunately fixed by the commit
>> e5e179aa3a39 ("pseries/drmem: don't cache node id in drmem_lmb struct").
> 
> Why can't we just backport that patch instead?  It's almost always
> better to do that than to have a one-off patch, as almost always those
> have bugs in them.

That's a good option too.
I was thinking that this 5.10 patch was not matching the stable release's 
guidelines since it was targeting performance issue, but since it is also fixing 
this issue, I'm certainly wrong.

So, forget that patch.

Thanks,
Laurent.