| Message ID | 20230317031339.10277-1-boqun.feng@gmail.com |
|---|---|
| Headers | show |
| Series | RCU-related lockdep changes for v6.4 | expand |
On Mon, Mar 20, 2023 at 01:13:05PM +0100, Peter Zijlstra wrote: > On Thu, Mar 16, 2023 at 08:13:36PM -0700, Boqun Feng wrote: > > Lock scenario print is always a weak spot of lockdep splats. Improvement > > can be made if we rework the dependency search and the error printing. > > > > However without touching the graph search, we can improve a little for > > the circular deadlock case, since we have the to-be-added lock > > dependency, and know whether these two locks are read/write/sync. > > > > In order to know whether a held_lock is sync or not, a bit was > > "stolen" from ->references, which reduce our limit for the same lock > > class nesting from 2^12 to 2^11, and it should still be good enough. > > > > Besides, since we now have bit in held_lock for sync, we don't need the > > "hardirqoffs being 1" trick, and also we can avoid the __lock_release() > > if we jump out of __lock_acquire() before the held_lock stored. > > > > With these changes, a deadlock case evolved with read lock and sync gets > > a better print-out from: > > > > [...] Possible unsafe locking scenario: > > [...] > > [...] CPU0 CPU1 > > [...] ---- ---- > > [...] lock(srcuA); > > [...] lock(srcuB); > > [...] lock(srcuA); > > [...] lock(srcuB); > > > > to > > > > [...] Possible unsafe locking scenario: > > [...] > > [...] CPU0 CPU1 > > [...] ---- ---- > > [...] rlock(srcuA); > > [...] lock(srcuB); > > [...] lock(srcuA); > > [...] sync(srcuB); > > > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com> > > --- > > include/linux/lockdep.h | 3 ++- > > kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++-------------- > > 2 files changed, 34 insertions(+), 17 deletions(-) > > > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h > > index 14d9dbedc6c1..b32256e9e944 100644 > > --- a/include/linux/lockdep.h > > +++ b/include/linux/lockdep.h > > @@ -134,7 +134,8 @@ struct held_lock { > > unsigned int read:2; /* see lock_acquire() comment */ > > unsigned int check:1; /* see lock_acquire() comment */ > > unsigned int hardirqs_off:1; > > - unsigned int references:12; /* 32 bits */ > > + unsigned int sync:1; > > + unsigned int references:11; /* 32 bits */ > > unsigned int pin_count; > > }; > > > > Yeah, I suppose we can do that -- another option is to steal some bits > from pin_count, but whatever (references used to be 11 a long while ago, > no problem going back to that). Thanks! > > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Applied locally. Regards, Boqun
Hi, This series enables deadlock detection for srcu_read_lock() vs synchronize_srcu(). Again, my first time helping prepare PR, so please take a careful look and yell at me if there is something wrong. Thanks a lot! You will also be able to find the series at: https://github/fbq/linux rcu/lockdep.2023.03.12a top commit is: 24390de55773 List of changes: Boqun Feng (4): locking/lockdep: Introduce lock_sync() rcu: Annotate SRCU's update-side lockdep dependencies locking: Reduce the number of locks in ww_mutex stress tests locking/lockdep: Improve the deadlock scenario print for sync and read lock Paul E. McKenney (3): rcutorture: Add SRCU deadlock scenarios rcutorture: Add RCU Tasks Trace and SRCU deadlock scenarios rcutorture: Add srcu_lockdep.sh include/linux/lockdep.h | 8 +- include/linux/srcu.h | 34 +++- kernel/locking/lockdep.c | 64 +++++- kernel/locking/test-ww_mutex.c | 2 +- kernel/rcu/rcutorture.c | 185 ++++++++++++++++++ kernel/rcu/srcutiny.c | 2 + kernel/rcu/srcutree.c | 2 + .../selftests/rcutorture/bin/srcu_lockdep.sh | 73 +++++++ 8 files changed, 359 insertions(+), 11 deletions(-) create mode 100755 tools/testing/selftests/rcutorture/bin/srcu_lockdep.sh