From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Andrea Parri <parri.andrea@gmail.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [RFC tip/locking/lockdep v6 19/20] rcu: Equip sleepable RCU with lockdep dependency graph checks
Date: Wed, 11 Apr 2018 11:57:30 -0700 [thread overview]
Message-ID: <20180411185730.GU3948@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180411135647.21496-1-boqun.feng@gmail.com>
On Wed, Apr 11, 2018 at 09:56:44PM +0800, Boqun Feng wrote:
> Although all flavors of RCU are annotated correctly with lockdep
> annotations as recursive read locks, the 'check' parameter for their
> calls to lock_acquire() is unset. Which means RCU read locks are not
> added into the lockdep dependency graph. This is fine for all flavors
> except sleepable RCU, because the deadlock scenarios for them are
> simple: calling synchronize_rcu() and its friends inside their read-side
> critical sections. But for sleepable RCU, as there may be multiple
> instances with multiple classes, there are more deadlock cases.
> Considering the following:
>
> TASK 1 TASK 2
> ======= ========
> i = srcu_read_lock(&sa); i = srcu_read_lock(&sb);
> synchronize_srcu(&sb); synchronize_srcu(&sa);
> srcu_read_unlock(&sa); srcu_read_unlock(&sb);
>
> Neither TASK 1 or 2 could go out of the read-side critical sections,
> because they are waiting for each other at synchronize_srcu().
>
> With the new improvement for lockdep, which allows us to detect
> deadlocks for recursive read locks, we can actually detect this. What we
> need to do are simply: a) mark srcu_read_{,un}lock() as 'check'
> lock_acquire() and b) annotate synchronize_srcu() as a empty
> grab-and-drop for a write lock (because synchronize_srcu() will wait for
> previous srcu_read_lock() to release, and won't block the next
> srcu_read_lock(), just like a empty write lock section).
>
> This patch adds those to allow we check deadlocks related to sleepable
> RCU with lockdep.
>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Very cool!
One question though... Won't this report a false-positive self-deadlock if
srcu_read_lock() is invoked from an interrupt handler?
Thanx, Paul
> ---
> include/linux/srcu.h | 51 +++++++++++++++++++++++++++++++++++++++++++++++++--
> kernel/rcu/srcutiny.c | 2 ++
> kernel/rcu/srcutree.c | 2 ++
> 3 files changed, 53 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index 33c1c698df09..23f397bd192c 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -99,6 +99,49 @@ static inline int srcu_read_lock_held(const struct srcu_struct *sp)
> return lock_is_held(&sp->dep_map);
> }
>
> +/**
> + * lockdep annotations for srcu_read_{un,}lock, and synchronize_srcu():
> + *
> + * srcu_read_lock() and srcu_read_unlock() are similar to rcu_read_lock() and
> + * rcu_read_unlock(), they are recursive read locks. But we mark them as
> + * "check", they will be added into lockdep dependency graph for deadlock
> + * detection. And we also annotate synchronize_srcu() as a
> + * write_lock()+write_unlock(), because synchronize_srcu() will wait for any
> + * corresponding previous srcu_read_lock() to release, and that acts like a
> + * empty grab-and-drop write lock.
> + *
> + * We do so because multiple sleepable rcu instances may cause deadlock as
> + * follow:
> + *
> + * Task 1:
> + * ia = srcu_read_lock(&srcu_A);
> + * synchronize_srcu(&srcu_B);
> + * srcu_read_unlock(&srcu_A, ia);
> + *
> + * Task 2:
> + * ib = srcu_read_lock(&srcu_B);
> + * synchronize_srcu(&srcu_A);
> + * srcu_read_unlock(&srcu_B, ib);
> + *
> + * And we want lockdep to detect this or more complicated deadlock with SRCU
> + * involved.
> + */
> +static inline void srcu_lock_acquire(struct lockdep_map *map)
> +{
> + lock_map_acquire_read(map);
> +}
> +
> +static inline void srcu_lock_release(struct lockdep_map *map)
> +{
> + lock_map_release(map);
> +}
> +
> +static inline void srcu_lock_sync(struct lockdep_map *map)
> +{
> + lock_map_acquire(map);
> + lock_map_release(map);
> +}
> +
> #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> static inline int srcu_read_lock_held(const struct srcu_struct *sp)
> @@ -106,6 +149,10 @@ static inline int srcu_read_lock_held(const struct srcu_struct *sp)
> return 1;
> }
>
> +#define srcu_lock_acquire(m) do { } while (0)
> +#define srcu_lock_release(m) do { } while (0)
> +#define srcu_lock_sync(m) do { } while (0)
> +
> #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> /**
> @@ -157,7 +204,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
> int retval;
>
> retval = __srcu_read_lock(sp);
> - rcu_lock_acquire(&(sp)->dep_map);
> + srcu_lock_acquire(&(sp)->dep_map);
> return retval;
> }
>
> @@ -171,7 +218,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
> static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
> __releases(sp)
> {
> - rcu_lock_release(&(sp)->dep_map);
> + srcu_lock_release(&(sp)->dep_map);
> __srcu_read_unlock(sp, idx);
> }
>
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 76ac5f50b2c7..bc89cb48d800 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -188,6 +188,8 @@ void synchronize_srcu(struct srcu_struct *sp)
> {
> struct rcu_synchronize rs;
>
> + srcu_lock_sync(&sp->dep_map);
> +
> init_rcu_head_on_stack(&rs.head);
> init_completion(&rs.completion);
> call_srcu(sp, &rs.head, wakeme_after_rcu);
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index d5cea81378cc..e2628e9275b9 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -997,6 +997,8 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
> */
> void synchronize_srcu(struct srcu_struct *sp)
> {
> + srcu_lock_sync(&sp->dep_map);
> +
> if (srcu_might_be_idle(sp) || rcu_gp_is_expedited())
> synchronize_srcu_expedited(sp);
> else
> --
> 2.16.2
>
next prev parent reply other threads:[~2018-04-11 20:00 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-11 13:50 [RFC tip/locking/lockdep v6 00/20] lockdep: Support deadlock detection for recursive read locks Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 01/20] lockdep/Documention: Recursive read lock detection reasoning Boqun Feng
2018-04-15 0:38 ` Randy Dunlap
2018-04-16 6:29 ` Boqun Feng
2018-04-27 13:50 ` Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 02/20] lockdep: Demagic the return value of BFS Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 03/20] lockdep: Make __bfs() visit every dependency until a match Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 04/20] lockdep: Redefine LOCK_*_STATE* bits Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 05/20] lockdep: Reduce the size of lock_list::distance Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 06/20] lockdep: Introduce lock_list::dep Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 07/20] lockdep: Extend __bfs() to work with multiple types of dependencies Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 08/20] lockdep: Make __bfs(.match) return bool Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 09/20] lockdep: Support deadlock detection for recursive read locks in check_noncircular() Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 10/20] lockdep: Adjust check_redundant() for recursive read change Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 11/20] lockdep: Fix recursive read lock related safe->unsafe detection Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 12/20] lockdep: Add recursive read locks into dependency graph Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 13/20] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 14/20] lockdep: Take read/write status in consideration when generate chainkey Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 15/20] lockdep/selftest: Unleash irq_read_recursion2 and add more Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 16/20] lockdep/selftest: Add more recursive read related test cases Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 17/20] Revert "locking/lockdep/selftests: Fix mixed read-write ABBA tests" Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 18/20] MAINTAINERS: Add myself as a LOCKING PRIMITIVES reviewer Boqun Feng
2018-04-11 13:56 ` [RFC tip/locking/lockdep v6 19/20] rcu: Equip sleepable RCU with lockdep dependency graph checks Boqun Feng
2018-04-11 18:57 ` Paul E. McKenney [this message]
2018-04-12 2:12 ` Boqun Feng
2018-04-12 9:12 ` Peter Zijlstra
2018-04-13 13:24 ` Boqun Feng
2018-04-11 13:57 ` [RFC tip/locking/lockdep v6 20/20] lockdep/selftest: Add a test case for SRCU Boqun Feng
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=20180411185730.GU3948@linux.vnet.ibm.com \
--to=paulmck@linux.vnet.ibm.com \
--cc=boqun.feng@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@redhat.com \
--cc=parri.andrea@gmail.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
/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).