Re: [PATCH v06 3/5] migration/memory: Add hotplug READD_MULTIPLE

On 10/16/2018 02:57 PM, Tyrel Datwyler wrote:

On 10/15/2018 05:39 PM, Michael Ellerman wrote:

quoted

Michael Bringmann [off-list ref] writes:

quoted

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 2b796da..9c76345 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c

@@ -541,6 +549,23 @@ static int dlpar_memory_readd_by_index(u32 drc_index)
 	return rc;
 }

+static int dlpar_memory_readd_multiple(void)
+{
+	struct drmem_lmb *lmb;
+	int rc;
+
+	pr_info("Attempting to update multiple LMBs\n");
+
+	for_each_drmem_lmb(lmb) {
+		if (drmem_lmb_update(lmb)) {
+			rc = dlpar_memory_readd_helper(lmb);
+			drmem_remove_lmb_update(lmb);
+		}
+	}
+
+	return rc;
+}

This leaves rc potentially uninitialised.

What should the result be in that case, -EINVAL ?

On another note if there are multiple LMBs to update the value of rc only reflects the final dlpar_memory_readd_helper() call.

Correct.  But that is what happens when we compress common code
between two disparate uses i.e. updating memory association after
a migration event with no reporting mechanism other than the console
log, vs re-adding a single LMB by index for the purposes of DLPAR / drmgr.

I could discard the return value from dlpar_memory_readd_helper entirely
in this function and just return 0, but in my experience, once errors start
to occur in memory dlpar ops, they tend to keep on occurring, so I was
returning the last one.  We could also make the code smart enough to
capture and return the first/last non-zero return code.  I didn't believe
that the frequency of errors for this operation warranted the overhead.

-Tyrel

Michael


-- 
Michael W. Bringmann
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