linux-kernel - Re: [PATCH v3 0/6] mm: Further memory block device cleanups

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Message-Id: <20190621164246.9a2354a571da41950bb74562@linux-foundation.org>
Date:   Fri, 21 Jun 2019 16:42:46 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Qian Cai <cai@....pw>, linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
        linux-mm@...ck.org, Andrew Banman <andrew.banman@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Arun KS <arunks@...eaurora.org>, Baoquan He <bhe@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Juergen Gross <jgross@...e.com>,
        Keith Busch <keith.busch@...el.com>,
        Len Brown <lenb@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "mike.travis@....com" <mike.travis@....com>,
        Oscar Salvador <osalvador@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Paul Mackerras <paulus@...ba.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rashmica Gupta <rashmica.g@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v3 0/6] mm: Further memory block device cleanups

On Fri, 21 Jun 2019 20:24:59 +0200 David Hildenbrand <david@...hat.com> wrote:

> @Qian Cai, unfortunately I can't reproduce.
> 
> If you get the chance, it would be great if you could retry with
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 972c5336bebf..742f99ddd148 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -868,6 +868,9 @@ int walk_memory_blocks(unsigned long start, unsigned
> long size,
>         unsigned long block_id;
>         int ret = 0;
> 
> +       if (!size)
> +               return;
> +
>         for (block_id = start_block_id; block_id <= end_block_id;
> block_id++) {
>                 mem = find_memory_block_by_id(block_id);
>                 if (!mem)
> 
> 
> 
> If both, start and size are 0, we would get a veeeery long loop. This
> would mean that we have an online node that does not span any pages at
> all (pgdat->node_start_pfn = 0, start_pfn + pgdat->node_spanned_pages = 0).

I think I'll make that a `return 0' and I won't drop patches 4-6 for
now, as we appear to have this fixed.



From: David Hildenbrand <david@...hat.com>
Subject: drivers-base-memoryc-get-rid-of-find_memory_block_hinted-v3-fix

handle zero-length walks

Link: http://lkml.kernel.org/r/1c2edc22-afd7-2211-c4c7-40e54e5007e8@redhat.com
Reported-by: Qian Cai <cai@....pw>
Tested-by: Qian Cai <cai@....pw>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 drivers/base/memory.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/base/memory.c~drivers-base-memoryc-get-rid-of-find_memory_block_hinted-v3-fix
+++ a/drivers/base/memory.c
@@ -866,6 +866,9 @@ int walk_memory_blocks(unsigned long sta
 	unsigned long block_id;
 	int ret = 0;
 
+	if (!size)
+		return 0;
+
 	for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
 		mem = find_memory_block_by_id(block_id);
 		if (!mem)