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b=tkcpWsQ6wQ6ft+VT1F4eerpYqic8MpMrWBidA6eNKsiaEuYYzbOBCnXiIjI9MPngY Bc3J4n5aYkUOXdje5HtrVyQQr5TJpUzkCy1vIM9+bsCW5JR8cDh8dsMoanlYWpLMo9 cBdJ/a/HvkXNNfhHF3kURONhqZwQq8HcSotl9qsI= Date: Tue, 18 Nov 2025 09:58:21 -0800 From: Andrew Morton To: Yuwen Chen Cc: senozhatsky@chromium.org, bgeffon@google.com, licayy@outlook.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, minchan@kernel.org, richardycc@google.com Subject: Re: [PATCH v2] zram: Fix the issue that the write - back limits might overflow Message-Id: <20251118095821.ebea2deea23aea6921866aa8@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 3F0AD40016 X-Stat-Signature: dixkxw599ef1b9398ridukrb9zwh5bi7 X-HE-Tag: 1763488705-912381 X-HE-Meta: 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 0ELMxOgo QocRc23FMCQMh6x+FrsqNbp/nsl5PcJPcHkKZZ/cFpesrWadOMutm8lqez+fyqEdATis34pn9jHk4kLkz9cQw+PWqiz3AZF57A11YNqBIefGwj0cJDVQu1drTsKTKwO9WNKmeccDdBVDfFmP3bv1XO39zJmk1YTGP6DxARGv87lgj9buYERXosJn7cE2aUbuQyQ7gOi49lUYDyPr5wwdxbSwP2bOSjGWSrDGAIdEH+e6AbsYYWVXrkZKFBJnNUgsfXyigkIkcDzpZ4nc63Wpx9Dp0CngdOlw+z6rcoWMyLhuIcIVPhGpIPa/LLw== 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 Tue, 18 Nov 2025 16:15:50 +0800 Yuwen Chen wrote: > Since the value of bd_wb_limit is an unsigned number, when the > page size is larger than 4 KB, it may cause an out-of-bounds situation. Please update the changelog to fully describe this out-of-bounds situation. Where does it occur, why, how, with what effects? > This patch fixes the issue by limiting bd_wb_limit to be an > integer multiple of PAGE_SIZE / 4096. I don't see at all how clearing the lower 11 bits is related to "page size is larger than 4 KB". All quite confusing! > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -579,6 +579,7 @@ static ssize_t writeback_limit_store(struct device *dev, > if (kstrtoull(buf, 10, &val)) > return ret; > > + val = val & (~((1UL << (PAGE_SHIFT - 12)) - 1)); Needs a little comment, I suggest. > down_write(&zram->init_lock); > zram->bd_wb_limit = val; > up_write(&zram->init_lock); > -- > 2.34.1