From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
elver@google.com, dvyukov@google.com,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 01/12] rcu: Add Kconfig option for strict RCU grace periods
Date: Wed, 12 Aug 2020 15:57:21 -0700 [thread overview]
Message-ID: <20200812225732.20068-1-paulmck@kernel.org> (raw)
In-Reply-To: <20200812225632.GA19759@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
People running automated tests have asked for a way to make RCU minimize
grace-period duration in order to increase the probability of KASAN
detecting a pointer being improperly leaked from an RCU read-side critical
section, for example, like this:
rcu_read_lock();
p = rcu_dereference(gp);
do_something_with(p); // OK
rcu_read_unlock();
do_something_else_with(p); // BUG!!!
The rcupdate.rcu_expedited boot parameter is a start in this direction,
given that it makes calls to synchronize_rcu() instead invoke the faster
(and more wasteful) synchronize_rcu_expedited(). However, this does
nothing to shorten RCU grace periods that are instead initiated by
call_rcu(), and RCU pointer-leak bugs can involve call_rcu() just as
surely as they can synchronize_rcu().
This commit therefore adds a RCU_STRICT_GRACE_PERIOD Kconfig option
that will be used to shorten normal (non-expedited) RCU grace periods.
This commit also dumps out a message when this option is in effect.
Later commits will actually shorten grace periods.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/Kconfig.debug | 15 +++++++++++++++
kernel/rcu/tree_plugin.h | 2 ++
2 files changed, 17 insertions(+)
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 3cf6132..cab5a4b 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -114,4 +114,19 @@ config RCU_EQS_DEBUG
Say N here if you need ultimate kernel/user switch latencies
Say Y if you are unsure
+config RCU_STRICT_GRACE_PERIOD
+ bool "Provide debug RCU implementation with short grace periods"
+ depends on DEBUG_KERNEL && RCU_EXPERT
+ default n
+ select PREEMPT_COUNT if PREEMPT=n
+ help
+ Select this option to build an RCU variant that is strict about
+ grace periods, making them as short as it can. This limits
+ scalability, destroys real-time response, degrades battery
+ lifetime and kills performance. Don't try this on large
+ machines, as in systems with more than about 10 or 20 CPUs.
+ But in conjunction with tools like KASAN, it can be helpful
+ when looking for certain types of RCU usage bugs, for example,
+ too-short RCU read-side critical sections.
+
endmenu # "RCU Debugging"
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index cb1e8c8..5c0c580 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -36,6 +36,8 @@ static void __init rcu_bootup_announce_oddness(void)
pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
if (IS_ENABLED(CONFIG_PROVE_RCU))
pr_info("\tRCU lockdep checking is enabled.\n");
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\n");
if (RCU_NUM_LVLS >= 4)
pr_info("\tFour(or more)-level hierarchy is enabled.\n");
if (RCU_FANOUT_LEAF != 16)
--
2.9.5
next prev parent reply other threads:[~2020-08-12 22:58 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 22:56 [PATCH tip/core/rcu 0/12] Add strict short-grace-period Kconfig option Paul E. McKenney
2020-08-12 22:57 ` paulmck [this message]
2020-08-12 22:57 ` [PATCH tip/core/rcu 02/12] rcu: Reduce leaf fanout for strict RCU grace periods paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 03/12] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 04/12] rcu: Force DEFAULT_RCU_BLIMIT to 1000 " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 05/12] rcu: Always set .need_qs from __rcu_read_lock() for strict GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 06/12] rcu: Do full report for .need_qs " paulmck
2020-08-13 0:50 ` Jann Horn
2020-08-13 3:29 ` Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 07/12] rcu: Attempt QS when CPU discovers GP " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 08/12] rcu: IPI all CPUs at GP start " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 09/12] rcu: IPI all CPUs at GP end " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 10/12] rcu: Provide optional RCU-reader exit delay " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 11/12] rcu: Execute RCU reader shortly after rcu_core " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 12/12] rcu: Report QS for outermost PREEMPT=n rcu_read_unlock() " paulmck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200812225732.20068-1-paulmck@kernel.org \
--to=paulmck@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=dhowells@redhat.com \
--cc=dipankar@in.ibm.com \
--cc=dvyukov@google.com \
--cc=edumazet@google.com \
--cc=elver@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).