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Mon, 31 Aug 2026 01:38:04 -0700 (PDT) Message-ID: Date: Mon, 31 Aug 2026 16:37:55 +0800 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.0 Subject: Re: [PATCH v2] zram: fix idle age_sec underflow in idle_store() To: Sergey Senozhatsky , Andrew Morton Cc: Hao Jia , minchan@kernel.org, axboe@kernel.dk, bgeffon@google.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, stable@vger.kernel.org References: <20260828083149.45760-1-jiahao.kernel@gmail.com> <20260828102446.3eb7f3dc779753b831e33fe6@linux-foundation.org> From: Hao Jia In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2026/8/31 12:15, Sergey Senozhatsky wrote: > On (26/08/28 10:24), Andrew Morton wrote: >> On Fri, 28 Aug 2026 16:31:49 +0800 Hao Jia wrote: > [..] >> >> Thanks. Sashiko asked a couple of questions about this change: >> https://sashiko.dev/#/patchset/20260828083149.45760-1-jiahao.kernel@gmail.com > > >> Does this early return prevent marking valid boot-time pages as idle? >> When a page is accessed during the first second of system boot, its ac_time >> would be 0. > > There is no possibility for zram to hold pages during first second of > system boot, regardless of whether zram was configured as a swap device > or as a block device (mount-ed with real filesystem). > > >> Can the early return above bypass this zram device initialization check? > > We already do that, e.g. when kstrtouint(buf, 0, &age_sec) fails. Apart > from that, that's not how one checks if device was initialized. We may > want to consolidate those checks, just for symmetry. Agreed on both points -- the early return is not a new "bypass", and the write() return value was never a way to probe init state. How about moving the init_done() check to the top, so all the early returns sit behind the same device-state check? static ssize_t idle_store(...) { struct zram *zram = dev_to_zram(dev); time64_t cutoff = 0; guard(rwsem_read)(&zram->dev_lock); if (!init_done(zram)) return -EINVAL; if (!sysfs_streq(buf, "all")) { ... } mark_idle(zram, cutoff); return len; } The read lock then also covers the parsing, but that is non-sleeping and its cost is negligible. Thanks, Hao