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Mon, 31 Mar 2025 11:19:38 -0400 X-MC-Unique: DXiJ7LEvNKCMMy60WETe5A-1 X-Mimecast-MFC-AGG-ID: DXiJ7LEvNKCMMy60WETe5A_1743434377 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8F693195608D; Mon, 31 Mar 2025 15:19:36 +0000 (UTC) Received: from localhost (unknown [10.72.112.9]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1A4331955DCE; Mon, 31 Mar 2025 15:19:34 +0000 (UTC) Date: Mon, 31 Mar 2025 23:19:28 +0800 From: Baoquan He To: Oscar Salvador Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/7] mm/gup: Fix the outdated code comments above get_user_pages_unlocked() Message-ID: References: <20250330121718.175815-1-bhe@redhat.com> <20250330121718.175815-4-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 224EE180009 X-Stat-Signature: efgfxramcfzs5bam6itxq573f8yy1h6s X-HE-Tag: 1743434382-206490 X-HE-Meta: U2FsdGVkX18WLDEf4m56cH2nzZBB41QdDoQ1PsOufryOG3mLs3yHk/fr+bnjje1ndn8fAtGvsKKvSxGlo9/4IlX0psHhvdn7v4OlSzOSKhOJ19F5hRroJt93WfMcC3xZWeQrutM5/YCMgJZsZ1zhkYyBpo7VroxmToZ3xMJS9VBnVBGVPTFp1AaVhSWjD7If29hBWNVo0AtuplmM8pw1bvQepquqBBmxV6E2GOZYI8dPPdu27d0zjdRiQ4WfQtwOBszzAbPzSocz+hU/lwIJNsEegEuzKSJvSbbQPVYgfFjjomXc3I+E9YT53+aO8vF3CYiOXV5FPPa5xdleyKIDs50Vw/a3Aq/UNqikFoLudcBZ3vMbkKqgMjgfJW4K1MZVllIg2+mVr92qsIKsdYRDhLJqecakk9SBGRTMrhLvQUVfQFj9jGCHn1VdEsOud/jCh92taaMceWkg/TEWIs9zhkdOk9mrQ2Jg2KcqliZXJ7xTPph9sWTkJXGJvzfDCLQaoFLijW9ux37/FZBBx3UiwL+Ehl71vwr4F3NPNAEweJWPx4l1wpr+r2LsBTMgl6lPdd61f2RXzdnXwjKGaeqBCBKw3zSr5AL58mSPjh0ozCf1zCTD1FXf4sADkmOz9gHYW6Xg3KduaZtp10CfjJW6W6+Hs75yG95aJ53KJQ+UG+9VY0l9/AnJr3pVEdSYlCB8q1cHlvQs6jaG+O4yaor1fvNQZaxSbWdegrqyLjGQXxH+Dxh8zN6BYqRzDGmCysWpiGl9hnGrDFRAtbCo6XCuqgPWKDfINdNL2NjBmLA6FAxOgP9cV0yAL5x3aP2eP6f6J8XnMokhNbM/UTIR7i5XxZPNBU40FzHblFO5SI7fGI2qOgV/Q4BpHDisbxVQWwIQQzv1tKfA4jOSdirW6n7wUHFEdkyCPj6UnldU+UEtBTcQ3TE9I/J4EOmND1NeBVJeOBCKRsPnh2UtcZp6Jq4 GJe6APuh y2Z4a76KvO7m/4EeazRi7Unb7J/yjUvOpckikxN2egnNeG95Suvruknn2vILcBca/7MUobIVjhNRDEYCVsy1fZsjYVInoYlL++whARhdxCT1pnC6Uq3nMXAzjB3ujkmD/UrmJVU3neFk+/iiAtvAtcfXoTDr0euwgY0AvUcMDS3bI2i3r5AzHBj+eLd0wNAsFTTx3ZLAlcIOc/7QJPitPEYe3wwtK8QIlMeJKkeBg+iyDFr6wLMZCNpb90jnagWphWfdu59KNfgiI3tNlqJgSkqzEdrWW282OAT/CwB6JuLyuL1+vrvl7rX/XoLYAbAX2YJhrD1+IqGxexQ4vQrEej7wNHQmvArVVtZleQTYAjIXYR5Mp2t9aqNl3LQ+Icy8FzeMgPFx2b8+u1N7tcQ4tH0sJbJfAUQusClrHNrrEe6GCnuKkM+19HJfBbsdn/pLcSCgUJgceioY9dTx7LidXszRFfkriq9P2Gi96 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 03/31/25 at 03:58pm, Oscar Salvador wrote: > On Sun, Mar 30, 2025 at 08:17:13PM +0800, Baoquan He wrote: > > Since commit f0818f472d8d ("mm: gup: add get_user_pages_locked > > and get_user_pages_unlocked"), get_user_pages() doesn't need to have > > mmap_lock held anymore. It calls __get_user_pages_locked() which > > can acquire and drop the mmap_lock internaly. > > Yes, __get_user_pages_locked() can aquire and drop the lock, but AFAICS > get_user_pages() always calls __get_user_pages_locked() with locked=1, > which means that is holding the lock, right? Ah, You are right. Thanks for looking into this, Oscar. I incredibly missed the local virable definition "int locked = 1;" line. I will drop this patch, or wrap the code comment fix into other patch about the obsolete reference with "get_user_pages(mm, ..., pages, NULL)". > > > Hence remove the incorrect code comments now. > > > > Signed-off-by: Baoquan He > > --- > > mm/gup.c | 16 +++------------- > > 1 file changed, 3 insertions(+), 13 deletions(-) > > > > diff --git a/mm/gup.c b/mm/gup.c > > index 8788105daee8..3345a065c2cb 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2702,19 +2702,9 @@ long get_user_pages(unsigned long start, unsigned long nr_pages, > > EXPORT_SYMBOL(get_user_pages); > > > > /* > > - * get_user_pages_unlocked() is suitable to replace the form: > > - * > > - * mmap_read_lock(mm); > > - * get_user_pages(mm, ..., pages, NULL); > > - * mmap_read_unlock(mm); > > - * > > - * with: > > - * > > - * get_user_pages_unlocked(mm, ..., pages); > > - * > > - * It is functionally equivalent to get_user_pages_fast so > > - * get_user_pages_fast should be used instead if specific gup_flags > > - * (e.g. FOLL_FORCE) are not required. > > + * get_user_pages_unlocked() is functionally equivalent to > > + * get_user_pages_fast so get_user_pages_fast should be used instead > > + * if specific gup_flags (e.g. FOLL_FORCE) are not required. > > */ > > long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > > struct page **pages, unsigned int gup_flags) > > -- > > 2.41.0 > > > > > > -- > Oscar Salvador > SUSE Labs >