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[2003:cb:c742:c800:d74f:aec6:f8ac:558]) by smtp.gmail.com with ESMTPSA id n21-20020a7bc5d5000000b003f42a75ac2asm8178149wmk.23.2023.05.22.05.07.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 May 2023 05:07:08 -0700 (PDT) Message-ID: <2ad811a6-899d-3be8-2bd3-29ebed3308a8@redhat.com> Date: Mon, 22 May 2023 14:07:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH -V2 5/5] swap: comments get_swap_device() with usage rule To: Huang Ying , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Johannes Weiner , Matthew Wilcox , Michal Hocko , Minchan Kim , Tim Chen , Yang Shi , Yu Zhao References: <20230522070905.16773-1-ying.huang@intel.com> <20230522070905.16773-6-ying.huang@intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230522070905.16773-6-ying.huang@intel.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DF50E140018 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: f3fxtat3c1i9hwargrsj9tysfn5egaut X-HE-Tag: 1684757231-333379 X-HE-Meta: U2FsdGVkX19w/hOZHicoLKl4SxTssSXo0TAHW2+neGWojRpPb6WeUlhtlWw5HXbcYEfP6m5DkV8I4KL1QXIeaBD9ueehcqNcRSupTc9zaZxzKrshX7yIrzm25Q0KL/5xv/xbkG5UQHB2jtAYT5Af8IGuHmn/b+182vWBaqXP1O6lm2t1KSMAASBbCv0k2SCw4bBO4zNxORcKDfZQ6B0EOAJXo8s8pgDSUajQZsoyw299ijpVbSgJ9/+7a0caFu6shB2LSezq7JF3zOMPdAKi+emg//glnE+fCwMyA2dngbBRGSxUcnNPXfv3MXiFxjkTM39OmAo48KLSEUWA6wEnxsuzFH84ysW/Ws4YRsRTl3Kq5SYwc5Qlz3O5rYGGi7PUxPXS6xD1ynptSx6RQNrDw0QIA8nDj1s+aoP6hFQdLKd9+Fih9wWpcixbc0XNc4yocLIBefn4sXv0T8wvq5AUE7M0cVgbFOEp+Cetf1kE2m+JzSuPxzwA6jkZ/O+lpl7BMxutbNrFzLNIkIcnLB8eSZ88yKm3j2HetmlYCkYNTO++ZW7NM2rwu2yfwkbIScTJiD5lRvN7GefRdV/YDVmOI4k5TgJzWHX6HfRstrlC9G4qhpH1mzV5g+9Hek936gW8Bho/cIls0eNzA32isWd0ToWEzpa1NRHRjZtfK3Haln+vvKWwvhfS5MPudcz1YW97+BhjJl2+Kmffn93Do7hK37FQZ7N4mUB77UyJIMmXU0LZT030R9XwfmAjODUQnrrpm55d335fZNjO2/Zz3szK396tcRIX5ksrdxQ8RNmAyvvKXu8JN7anGYe8vgh90lWDVfHU/nfosL4Dq/XiY0emfBYR51KnfldTC9HZaDmBEqmspaKwMdUka20ATyHb/GkakUrFrkbNUBpjRv2uoXx9FIxSIyly/p7Y1C+KyJU0IegvIHKX3f77Ei7seBi23kNazyZkryYira9SrRvHEXx OPWWSK/V 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 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: On 22.05.23 09:09, Huang Ying wrote: > The general rule to use a swap entry is as follows. > > When we get a swap entry, if there isn't some other way to prevent > swapoff, such as page lock for swap cache, page table lock, etc., the > swap entry may become invalid because of swapoff. Then, we need to > enclose all swap related functions with get_swap_device() and > put_swap_device(), unless the swap functions call > get/put_swap_device() by themselves. > > Add the rule as comments of get_swap_device(). > > Signed-off-by: "Huang, Ying" > Cc: David Hildenbrand > Cc: Hugh Dickins > Cc: Johannes Weiner > Cc: Matthew Wilcox > Cc: Michal Hocko > Cc: Minchan Kim > Cc: Tim Chen > Cc: Yang Shi > Cc: Yu Zhao > --- > mm/swapfile.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 4dbaea64635d..0c1cb935b2eb 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1219,6 +1219,13 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p, > } > > /* > + * When we get a swap entry, if there isn't some other way to prevent > + * swapoff, such as page lock for swap cache, page table lock, etc., Again "page lock for swap cache" might be imprecise. > + * the swap entry may become invalid because of swapoff. Then, we > + * need to enclose all swap related functions with get_swap_device() > + * and put_swap_device(), unless the swap functions call > + * get/put_swap_device() by themselves. > + * > * Check whether swap entry is valid in the swap device. If so, > * return pointer to swap_info_struct, and keep the swap entry valid > * via preventing the swap device from being swapoff, until > @@ -1227,9 +1234,8 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p, > * Notice that swapoff or swapoff+swapon can still happen before the > * percpu_ref_tryget_live() in get_swap_device() or after the > * percpu_ref_put() in put_swap_device() if there isn't any other way > - * to prevent swapoff, such as page lock, page table lock, etc. The > - * caller must be prepared for that. For example, the following > - * situation is possible. > + * to prevent swapoff. The caller must be prepared for that. For > + * example, the following situation is possible. > * > * CPU1 CPU2 > * do_swap_page() Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb