From: "Joel Fernandes (Google)" <joel@joelfernandes.org> To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>, Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>, Bjorn Helgaas <bhelgaas@google.com>, Borislav Petkov <bp@alien8.de>, c0d1n61at3@gmail.com, "David S. Miller" <davem@davemloft.net>, edumazet@google.com, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, Jonathan Corbet <corbet@lwn.net>, Josh Triplett <josh@joshtriplett.org>, keescook@chromium.org, kernel-hardening@lists.openwall.com, kernel-team@android.com, Lai Jiangshan <jiangshanlai@gmail.com>, Len Brown <lenb@kernel.org>, linux-acpi@vger.kernel.org, linux-doc@vger.kernel.org, linux-pci@vger.kernel.org, linux-pm@vger.kernel.org, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, neilb@suse.com, netdev@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>, "Paul E. McKenney" <paulmck@linux.ibm.com>, Pavel Machek <pavel@ucw.cz>, peterz@infradead.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Rasmus Villemoes <rasmus.villemoes@prevas.dk>, rcu@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, will@kernel.org, x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)) Subject: [PATCH v2 9/9] doc: Update documentation about list_for_each_entry_rcu Date: Fri, 12 Jul 2019 13:00:24 -0400 Message-ID: <20190712170024.111093-10-joel@joelfernandes.org> (raw) In-Reply-To: <20190712170024.111093-1-joel@joelfernandes.org> This patch updates the documentation with information about usage of lockdep with list_for_each_entry_rcu(). Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> --- Documentation/RCU/lockdep.txt | 15 +++++++++++---- Documentation/RCU/whatisRCU.txt | 9 ++++++++- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt index da51d3068850..3d967df3a801 100644 --- a/Documentation/RCU/lockdep.txt +++ b/Documentation/RCU/lockdep.txt @@ -96,7 +96,14 @@ other flavors of rcu_dereference(). On the other hand, it is illegal to use rcu_dereference_protected() if either the RCU-protected pointer or the RCU-protected data that it points to can change concurrently. -There are currently only "universal" versions of the rcu_assign_pointer() -and RCU list-/tree-traversal primitives, which do not (yet) check for -being in an RCU read-side critical section. In the future, separate -versions of these primitives might be created. +Similar to rcu_dereference_protected, The RCU list and hlist traversal +primitives also check for whether there are called from within a reader +section. However, an optional lockdep expression can be passed to them as +the last argument in case they are called under other non-RCU protection. + +For example, the workqueue for_each_pwq() macro is implemented as follows. +It is safe to call for_each_pwq() outside a reader section but under protection +of wq->mutex: +#define for_each_pwq(pwq, wq) + list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node, + lock_is_held(&(wq->mutex).dep_map)) diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 981651a8b65d..a08c03735963 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -290,7 +290,7 @@ rcu_dereference() at any time, including immediately after the rcu_dereference(). And, again like rcu_assign_pointer(), rcu_dereference() is typically used indirectly, via the _rcu list-manipulation - primitives, such as list_for_each_entry_rcu(). + primitives, such as list_for_each_entry_rcu() [2]. [1] The variant rcu_dereference_protected() can be used outside of an RCU read-side critical section as long as the usage is @@ -305,6 +305,13 @@ rcu_dereference() a lockdep splat is emitted. See RCU/Design/Requirements/Requirements.html and the API's code comments for more details and example usage. + [2] In case the list_for_each_entry_rcu() primitive is intended + to be used outside of an RCU reader section such as when + protected by a lock, then an additional lockdep expression can be + passed as the last argument to it so that RCU lockdep checking code + knows that the dereference of the list pointers are safe. If the + indicated protection is not provided, a lockdep splat is emitted. + The following diagram shows how each API communicates among the reader, updater, and reclaimer. -- 2.22.0.510.g264f2c817a-goog
prev parent reply index Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-07-12 17:00 [PATCH v2 0/9] Harden list_for_each_entry_rcu() and family Joel Fernandes (Google) 2019-07-12 17:00 ` [PATCH v2 1/9] rcu/update: Remove useless check for debug_locks Joel Fernandes (Google) 2019-07-12 17:00 ` [PATCH v2 2/9] rcu: Add support for consolidated-RCU reader checking Joel Fernandes (Google) 2019-07-16 18:22 ` Paul E. McKenney 2019-07-16 18:35 ` Joel Fernandes 2019-07-16 18:50 ` Paul E. McKenney 2019-07-12 17:00 ` [PATCH v2 3/9] rcu/sync: Remove custom check for reader-section Joel Fernandes (Google) 2019-07-12 21:35 ` Joel Fernandes 2019-07-12 23:32 ` Paul E. McKenney 2019-07-13 3:01 ` Joel Fernandes 2019-07-13 3:10 ` Joel Fernandes 2019-07-13 8:21 ` Paul E. McKenney 2019-07-13 13:30 ` Joel Fernandes 2019-07-13 14:41 ` Paul E. McKenney 2019-07-13 15:36 ` Joel Fernandes 2019-07-13 15:50 ` Paul E. McKenney 2019-07-13 16:13 ` Joel Fernandes 2019-07-13 21:28 ` Paul E. McKenney 2019-07-14 18:10 ` Joel Fernandes 2019-07-14 18:38 ` Joel Fernandes 2019-07-14 18:50 ` Paul E. McKenney 2019-07-15 7:26 ` Oleg Nesterov 2019-07-16 18:26 ` Paul E. McKenney 2019-07-16 18:28 ` Paul E. McKenney 2019-07-12 17:00 ` [PATCH v2 4/9] ipv4: add lockdep condition to fix for_each_entry Joel Fernandes (Google) 2019-07-12 17:00 ` [PATCH v2 5/9] driver/core: Convert to use built-in RCU list checking Joel Fernandes (Google) 2019-07-12 17:00 ` [PATCH v2 6/9] workqueue: Convert for_each_wq to use built-in list check Joel Fernandes (Google) 2019-07-12 17:00 ` [PATCH v2 7/9] x86/pci: Pass lockdep condition to pcm_mmcfg_list iterator Joel Fernandes (Google) 2019-07-12 17:00 ` [PATCH v2 8/9] acpi: Use built-in RCU list checking for acpi_ioremaps list Joel Fernandes (Google) 2019-07-12 17:00 ` Joel Fernandes (Google) [this message]
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