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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783366465; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6FIHHLRwVR4NtU0/LL0GRJyj4HVJuRDsfXvwLZzguVw=; b=IZEhSE9Hn+GAtySFANf8zpZy70wX6zakvqMszh5suNaxs2g92mI7HXIFOX3/tWNbIX/g6g HCrJ7FoS8rGGkXvqTUWDdbpCKNlSnIIH8FyGQ+xZwDBDSycvLiijeo5LJnMO7kTMbu5b7l ZfA89c/n1BImcgpi83k/4cTN/4yc6XM= From: Usama Arif To: Nico Pache Cc: Usama Arif , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, David Hildenbrand , Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan Subject: Re: [PATCH 6/8] mm/khugepaged: unmap pte before releasing vma write lock Date: Mon, 6 Jul 2026 12:34:06 -0700 Message-ID: <20260706193407.825323-1-usama.arif@linux.dev> In-Reply-To: <20260706154500.39178-7-npache@redhat.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1880E1C0002 X-Stat-Signature: nkwzuwb3orm9bogojpxh3g4y6jc8geda X-HE-Tag: 1783366467-47177 X-HE-Meta: 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 g0u+/1I2 0Epu4WOaPecK40z9O4YshwzRuE5modIUFfFckXNZkErUvltrGN2MHOPNTULV1ObXnXpQG9RwSz3SvJsu4ppQQfYT3qv9+pE5qbwEwZegrveS2DlEedaPAmIvyFzXmpCEgVu7IfM2s+jCoZ5l0zWpj0IJBc5OFWx+21UBSXmzBwIu0NGguckA2sgtAlisc2h2llKk/3APXhTncKtB5Gg3PSSC3h0mVzMnWK8uNAXcUMXBx0fEvuLtcm8EnCg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 6 Jul 2026 09:44:53 -0600 Nico Pache wrote: > We are currently dropping the anon_vma write lock before unmapping the > PTE. Although this is safe, due to us still holding the mmap_write_lock, > its safer and less confusing to switch the order of these two operations. > > Suggested-by: David Hildenbrand > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Would it not be better to add a comment here why its safe to do so, instead of extending lock hold period? I think its more confusing to hold a lock for longer than we should. > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index c4ea2dc1591b..3c6f1254deca 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1548,10 +1548,10 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long s > > result = SCAN_SUCCEED; > out_up_write: > - if (anon_vma_locked) > - anon_vma_unlock_write(vma->anon_vma); > if (pte) > pte_unmap(pte); > + if (anon_vma_locked) > + anon_vma_unlock_write(vma->anon_vma); > mmap_write_unlock(mm); > out_nolock: > if (folio) > -- > 2.54.0 > >