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[93.41.0.79]) by smtp.gmail.com with ESMTPSA id v18-20020a50a452000000b004c3e3a6136dsm8404626edb.21.2023.03.22.18.38.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 18:38:32 -0700 (PDT) From: Andrea Parri To: stern@rowland.harvard.edu, will@kernel.org, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, paulmck@kernel.org, akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Andrea Parri Subject: [PATCH] tools/memory-model: Remove out-of-date SRCU documentation Date: Thu, 23 Mar 2023 02:37:51 +0100 Message-Id: <20230323013751.77588-1-parri.andrea@gmail.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Spam-Status: No, score=-0.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1761122110954888919?= X-GMAIL-MSGID: =?utf-8?q?1761122110954888919?= Commit 6cd244c87428 ("tools/memory-model: Provide exact SRCU semantics") changed the semantics of partially overlapping SRCU read-side critical sections (among other things), making such documentation out-of-date. The new, semantic changes are discussed in explanation.txt. Remove the out-of-date documentation. Signed-off-by: Andrea Parri Reviewed-by: Joel Fernandes (Google) Acked-by: Alan Stern --- .../Documentation/litmus-tests.txt | 27 +------------------ 1 file changed, 1 insertion(+), 26 deletions(-) diff --git a/tools/memory-model/Documentation/litmus-tests.txt b/tools/memory-model/Documentation/litmus-tests.txt index 26554b1c5575e..acac527328a1f 100644 --- a/tools/memory-model/Documentation/litmus-tests.txt +++ b/tools/memory-model/Documentation/litmus-tests.txt @@ -1028,32 +1028,7 @@ Limitations of the Linux-kernel memory model (LKMM) include: additional call_rcu() process to the site of the emulated rcu-barrier(). - e. Although sleepable RCU (SRCU) is now modeled, there - are some subtle differences between its semantics and - those in the Linux kernel. For example, the kernel - might interpret the following sequence as two partially - overlapping SRCU read-side critical sections: - - 1 r1 = srcu_read_lock(&my_srcu); - 2 do_something_1(); - 3 r2 = srcu_read_lock(&my_srcu); - 4 do_something_2(); - 5 srcu_read_unlock(&my_srcu, r1); - 6 do_something_3(); - 7 srcu_read_unlock(&my_srcu, r2); - - In contrast, LKMM will interpret this as a nested pair of - SRCU read-side critical sections, with the outer critical - section spanning lines 1-7 and the inner critical section - spanning lines 3-5. - - This difference would be more of a concern had anyone - identified a reasonable use case for partially overlapping - SRCU read-side critical sections. For more information - on the trickiness of such overlapping, please see: - https://paulmck.livejournal.com/40593.html - - f. Reader-writer locking is not modeled. It can be + e. Reader-writer locking is not modeled. It can be emulated in litmus tests using atomic read-modify-write operations.