From patchwork Tue Nov 30 15:27:55 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Daniel Vetter X-Patchwork-Id: 517325 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 724F1C433F5 for ; Tue, 30 Nov 2021 15:28:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230465AbhK3Pb2 (ORCPT ); Tue, 30 Nov 2021 10:31:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229865AbhK3PbV (ORCPT ); Tue, 30 Nov 2021 10:31:21 -0500 Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DE6AC061574 for ; Tue, 30 Nov 2021 07:28:02 -0800 (PST) Received: by mail-ed1-x52c.google.com with SMTP id w1so88596301edc.6 for ; Tue, 30 Nov 2021 07:28:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=KUG8ZDNwLQ9mug9AKEG2rtiTG0/UXMwSxpSjHiH+UNE=; b=A6HBiWYKyW2FkPzZmHTApcwlV2pu8P3ubUaEmWvCN3eeBrGVpyEk65p/g/xvRiw+jz nK5A/HZwmdz9h/JbT6JbbKdAFvxVYH5K7/kJZMF27u4k6Pzw7dvdZ0E9b/5HFxmQLy2Z btMYzH92aZgv4g4mtWoOsvCINFWCvczqgEn+E= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=KUG8ZDNwLQ9mug9AKEG2rtiTG0/UXMwSxpSjHiH+UNE=; b=qcsGbKuRvh0EGZg6EC14HzXcnv43K0Fe6E4Rt6+ZamBuZ0POtpH+n5DaSZ7RzXRfZ+ 04hP+vUmody72zURX4zZuICgneqGvlivdBM1SZ9f+5y97MSdzePzYMs2CLKkRZQZb+H8 cdLgboXgocvSczrq29vt1/isbtnyRgWGW5JjOeVcwBxE5oU/vi+CfVzYVZx+3Rj/Jryo b7rht1KJtXjEjMAkm8fTMXro2Em3UdDmeBr3IuyGBL3ncxmgNFI6WTE2VL2zzIA0xFAa mZm1Vv0YbSXAYN+kNuu2vvRoOiSsbZJtz0hmVw+cotbdW4cVg9OQ5YKRWpsURw5fYpNV 70cg== X-Gm-Message-State: AOAM531ScMTz3j2DIiIfgf2q6lBjG1lgSOOHVjVps2rlaTwsVUxK8H2r TNtHTbcsxkssLSkGoy89K/I8Vw== X-Google-Smtp-Source: ABdhPJxnvA8DcF3dnAQORTrpJZDY364vc8s5H8Qf7UOGl3epYBfx5zwFZ1uG/Cmss6f6K+CCHcY3sg== X-Received: by 2002:a50:fb16:: with SMTP id d22mr85823229edq.367.1638286081094; Tue, 30 Nov 2021 07:28:01 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id lk22sm9342990ejb.83.2021.11.30.07.28.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Nov 2021 07:28:00 -0800 (PST) From: Daniel Vetter To: DRI Development Cc: Daniel Vetter , =?utf-8?q?Christian_K=C3=B6nig?= , Daniel Vetter , Sumit Semwal , linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org Subject: [PATCH] dma-resv: some doc polish for iterators Date: Tue, 30 Nov 2021 16:27:55 +0100 Message-Id: <20211130152756.1388106-1-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20211130091609.1335915-1-daniel.vetter@ffwll.ch> References: <20211130091609.1335915-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hammer it a bit more in that iterators can be restarted and when that matters, plus suggest to prefer the locked version whenver. Also delete the two leftover kerneldoc for static functions plus sprinkle some more links while at it. v2: Keep some comments (Christian) Reviewed-by: Christian König Signed-off-by: Daniel Vetter Cc: Sumit Semwal Cc: "Christian König" Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org --- drivers/dma-buf/dma-resv.c | 29 +++++++++++++++-------------- include/linux/dma-resv.h | 13 ++++++++++++- 2 files changed, 27 insertions(+), 15 deletions(-) diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 9eb2baa387d4..a62eb8fc33b9 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -323,12 +323,8 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence) } EXPORT_SYMBOL(dma_resv_add_excl_fence); -/** - * dma_resv_iter_restart_unlocked - restart the unlocked iterator - * @cursor: The dma_resv_iter object to restart - * - * Restart the unlocked iteration by initializing the cursor object. - */ +/* Restart the iterator by initializing all the necessary fields, but not the + * relation to the dma_resv object. */ static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor) { cursor->seq = read_seqcount_begin(&cursor->obj->seq); @@ -344,14 +340,7 @@ static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor) cursor->is_restarted = true; } -/** - * dma_resv_iter_walk_unlocked - walk over fences in a dma_resv obj - * @cursor: cursor to record the current position - * - * Return all the fences in the dma_resv object which are not yet signaled. - * The returned fence has an extra local reference so will stay alive. - * If a concurrent modify is detected the whole iteration is started over again. - */ +/* Walk to the next not signaled fence and grab a reference to it */ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor) { struct dma_resv *obj = cursor->obj; @@ -387,6 +376,12 @@ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor) * dma_resv_iter_first_unlocked - first fence in an unlocked dma_resv obj. * @cursor: the cursor with the current position * + * Subsequent fences are iterated with dma_resv_iter_next_unlocked(). + * + * Beware that the iterator can be restarted. Code which accumulates statistics + * or similar needs to check for this with dma_resv_iter_is_restarted(). For + * this reason prefer the locked dma_resv_iter_first() whenver possible. + * * Returns the first fence from an unlocked dma_resv obj. */ struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor) @@ -406,6 +401,10 @@ EXPORT_SYMBOL(dma_resv_iter_first_unlocked); * dma_resv_iter_next_unlocked - next fence in an unlocked dma_resv obj. * @cursor: the cursor with the current position * + * Beware that the iterator can be restarted. Code which accumulates statistics + * or similar needs to check for this with dma_resv_iter_is_restarted(). For + * this reason prefer the locked dma_resv_iter_next() whenver possible. + * * Returns the next fence from an unlocked dma_resv obj. */ struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor) @@ -431,6 +430,8 @@ EXPORT_SYMBOL(dma_resv_iter_next_unlocked); * dma_resv_iter_first - first fence from a locked dma_resv object * @cursor: cursor to record the current position * + * Subsequent fences are iterated with dma_resv_iter_next_unlocked(). + * * Return the first fence in the dma_resv object while holding the * &dma_resv.lock. */ diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index dbd235ab447f..ebe908592ac3 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -153,6 +153,13 @@ struct dma_resv { * struct dma_resv_iter - current position into the dma_resv fences * * Don't touch this directly in the driver, use the accessor function instead. + * + * IMPORTANT + * + * When using the lockless iterators like dma_resv_iter_next_unlocked() or + * dma_resv_for_each_fence_unlocked() beware that the iterator can be restarted. + * Code which accumulates statistics or similar needs to check for this with + * dma_resv_iter_is_restarted(). */ struct dma_resv_iter { /** @obj: The dma_resv object we iterate over */ @@ -243,7 +250,11 @@ static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor) * &dma_resv.lock and using RCU instead. The cursor needs to be initialized * with dma_resv_iter_begin() and cleaned up with dma_resv_iter_end(). Inside * the iterator a reference to the dma_fence is held and the RCU lock dropped. - * When the dma_resv is modified the iteration starts over again. + * + * Beware that the iterator can be restarted when the struct dma_resv for + * @cursor is modified. Code which accumulates statistics or similar needs to + * check for this with dma_resv_iter_is_restarted(). For this reason prefer the + * lock iterator dma_resv_for_each_fence() whenever possible. */ #define dma_resv_for_each_fence_unlocked(cursor, fence) \ for (fence = dma_resv_iter_first_unlocked(cursor); \