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To: Qiang Liu , baolin.wang@linux.alibaba.com, Kemeng Shi , Baolin Wang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20241114065720.3665-1-liuq131@chinatelecom.cn> Content-Language: en-US From: Vlastimil Babka In-Reply-To: <20241114065720.3665-1-liuq131@chinatelecom.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E135B804D6 X-Stat-Signature: shyocrw5ptdzorazi8a5krmhnhii1ipi X-Rspam-User: X-HE-Tag: 1731570199-459102 X-HE-Meta: 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 hOA92nwR Zm1ikdItCOR5ZQijtxatkMVVPBLJIUPJkCR+R5n1Pc7yGtyFoVkKMk3SBDP88GH6azDEb4rbzrBG+LMdiO8HybWqL4YkixzQZK/1JOOGKUE8F81pNiD3ZHSxxsdQ/y9Wgfq17luRAQc5nicErxi4piUBE9eBj2LCDOHMXfM82SCGxf0HRN+grh5KGY8KaTjXizf8MlyFEKVgnkRLA6SpY7kPK120BC9yqOjUwp9MbGwO7+UeJU+z5CfGZHg5mkmkS+n760snFYWI7dLgs2nnQOsmsE3tnFRzXoz8y X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/14/24 07:57, Qiang Liu wrote: > It is impossible for the situation where blockpfn > end_pfn to arise, > The if statement here is not only unnecessary, but may also lead to > a misunderstanding that blockpfn > end_pfn could potentially happen. > so these unnecessary checking code should be removed. > > Signed-off-by: Qiang Liu I see that's since 3da0272a4c7d ("mm/compaction: correctly return failure with bogus compound_order in strict mode") I think that commit introduced a risk of overflow due to a bogus order (which we read in a racy way), and once blockpfn overflows it will satisfy <= end_pfn and might e.g. end up scanning a completely different zone? if (blockpfn + (1UL << order) <= end_pfn) { blockpfn += (1UL << order) - 1; page += (1UL << order) - 1; nr_scanned += (1UL << order) - 1; } We should better add back the MAX_ORDER sanity check? > --- > mm/compaction.c | 6 ------ > 1 file changed, 6 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index a2b16b08cbbf..baeda7132252 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -682,12 +682,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > if (locked) > spin_unlock_irqrestore(&cc->zone->lock, flags); > > - /* > - * Be careful to not go outside of the pageblock. > - */ > - if (unlikely(blockpfn > end_pfn)) > - blockpfn = end_pfn; > - > trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn, > nr_scanned, total_isolated); >