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 [thread overview]
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 other threads:[~2019-07-12 17:01 UTC|newest]
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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