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([2602:47:d490:6901:1eed:f77f:f320:8b14]) by smtp.gmail.com with ESMTPSA id a4-20020a170902ecc400b001b8b4730355sm1754714plh.287.2023.08.04.06.41.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Aug 2023 06:41:34 -0700 (PDT) Message-ID: <04b4edc5-f24d-3d33-970a-172e889d9c02@linaro.org> Date: Fri, 4 Aug 2023 06:41:31 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PULL 02/10] util/interval-tree: Use qatomic_set_mb in rb_link_node Content-Language: en-US To: Michael Tokarev , qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Peter Maydell References: <20230731210211.137353-1-richard.henderson@linaro.org> <20230731210211.137353-3-richard.henderson@linaro.org> <8854030f-73ea-b92b-2ee4-c219acfbe1c3@tls.msk.ru> From: Richard Henderson In-Reply-To: <8854030f-73ea-b92b-2ee4-c219acfbe1c3@tls.msk.ru> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::62d; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x62d.google.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.093, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 8/4/23 02:02, Michael Tokarev wrote: > 01.08.2023 00:02, Richard Henderson wrote: >> Ensure that the stores to rb_left and rb_right are complete before >> inserting the new node into the tree.  Otherwise a concurrent reader >> could see garbage in the new leaf. >> >> Cc: qemu-stable@nongnu.org >> Reviewed-by: Peter Maydell >> Signed-off-by: Richard Henderson >> --- >>   util/interval-tree.c | 6 +++++- >>   1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/util/interval-tree.c b/util/interval-tree.c >> index 5a0ad21b2d..759562db7d 100644 >> --- a/util/interval-tree.c >> +++ b/util/interval-tree.c >> @@ -128,7 +128,11 @@ static inline void rb_link_node(RBNode *node, RBNode *parent, >> RBNode **rb_link) >>       node->rb_parent_color = (uintptr_t)parent; >>       node->rb_left = node->rb_right = NULL; >> -    qatomic_set(rb_link, node); >> +    /* >> +     * Ensure that node is initialized before insertion, >> +     * as viewed by a concurrent search. >> +     */ >> +    qatomic_set_mb(rb_link, node); > > FWIW, there's no qatomic_set_mb() in 8.0 and before, so this can not be > directly applied to stable-8.0.  This commit is missing in 8.0 before > qatomic_set_mb() can be used: > > commit 06831001ac8949b0801e0d20c347d97339769a20 > Author: Paolo Bonzini > Date:   Fri Mar 3 14:37:51 2023 +0100 > >     atomics: eliminate mb_read/mb_set > > I don't think it's a good idea to back-port this commit to stable-8.0. > > How do you think we can solve this for 8.0? The function is called qatomic_mb_set instead of qatomic_set_mb in stable-8.0. r~