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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1690471295; 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; bh=IlwsvGNRJnMmWnx4X81rM4zHsMyVpGxID3lfp4Wm+1A=; b=UnKls/jjqZcZzftvuk3ljzIPLwoprqIWOu7LoFbkkVSAIBhLiG4rj7MDXbC/wSvtMI359l N6V7bn3EnXoWjtBGCXe0jAO/FTTa0piMOgDtLsfDpCDWkAJsdhdkz/EHKYdP3PVjE+UdzQ hRtC43R6653je6/DHV9wtgV6FW0mNXk= From: chengming.zhou@linux.dev To: axboe@kernel.dk, osandov@fb.com, ming.lei@redhat.com, kbusch@kernel.org, krisman@suse.de Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com Subject: [PATCH v2 1/3] sbitmap: fix hint wrap in the failure case Date: Thu, 27 Jul 2023 23:20:18 +0800 Message-ID: <20230727152020.3633009-1-chengming.zhou@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1772591240811883189 X-GMAIL-MSGID: 1772591240811883189 From: Chengming Zhou ``` hint = nr + 1; if (hint >= depth - 1) hint = 0; ``` Now we wrap the hint to 0 in the failure case, but has two problems: 1. hint == depth - 1, is actually an available offset hint, in which case we shouldn't wrap hint to 0. 2. In the strict round_robin non-wrap case, we shouldn't wrap at all. ``` wrap = wrap && hint; ``` We only need to check wrap based on the original hint ( > 0), don't need to recheck the new hint which maybe updated in the failure case, which may cause second wrap. We set wrap to false after we wrap once to avoid repeated wrap, which is clearer than rechecking the hint. Signed-off-by: Chengming Zhou --- lib/sbitmap.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index d0a5081dfd12..ac4027884765 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -149,7 +149,8 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth, * offset to 0 in a failure case, so start from 0 to * exhaust the map. */ - if (hint && wrap) { + if (wrap) { + wrap = false; hint = 0; continue; } @@ -160,8 +161,14 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth, break; hint = nr + 1; - if (hint >= depth - 1) - hint = 0; + if (unlikely(hint >= depth)) { + if (wrap) { + wrap = false; + hint = 0; + continue; + } + return -1; + } } return nr;