From: Peter Zijlstra <peterz@infradead.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Andrea Parri <parri.andrea@gmail.com>
Subject: Re: [RFC tip/locking/lockdep v5 04/17] lockdep: Introduce lock_list::dep
Date: Fri, 23 Feb 2018 12:55:20 +0100 [thread overview]
Message-ID: <20180223115520.GV25181@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180222070904.548-5-boqun.feng@gmail.com>
On Thu, Feb 22, 2018 at 03:08:51PM +0800, Boqun Feng wrote:
> @@ -1012,6 +1013,33 @@ static inline bool bfs_error(enum bfs_result res)
> return res < 0;
> }
>
> +#define DEP_NN_BIT 0
> +#define DEP_RN_BIT 1
> +#define DEP_NR_BIT 2
> +#define DEP_RR_BIT 3
> +
> +#define DEP_NN_MASK (1U << (DEP_NN_BIT))
> +#define DEP_RN_MASK (1U << (DEP_RN_BIT))
> +#define DEP_NR_MASK (1U << (DEP_NR_BIT))
> +#define DEP_RR_MASK (1U << (DEP_RR_BIT))
> +
> +static inline unsigned int __calc_dep_bit(int prev, int next)
> +{
> + if (prev == 2 && next != 2)
> + return DEP_RN_BIT;
> + if (prev != 2 && next == 2)
> + return DEP_NR_BIT;
> + if (prev == 2 && next == 2)
> + return DEP_RR_BIT;
> + else
> + return DEP_NN_BIT;
> +}
> +
> +static inline unsigned int calc_dep(int prev, int next)
> +{
> + return 1U << __calc_dep_bit(prev, next);
> +}
> +
> static enum bfs_result __bfs(struct lock_list *source_entry,
> void *data,
> int (*match)(struct lock_list *entry, void *data),
> @@ -1921,6 +1949,16 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
> if (entry->class == hlock_class(next)) {
> if (distance == 1)
> entry->distance = 1;
> + entry->dep |= calc_dep(prev->read, next->read);
> + }
> + }
> +
> + /* Also, update the reverse dependency in @next's ->locks_before list */
> + list_for_each_entry(entry, &hlock_class(next)->locks_before, entry) {
> + if (entry->class == hlock_class(prev)) {
> + if (distance == 1)
> + entry->distance = 1;
> + entry->dep |= calc_dep(next->read, prev->read);
> return 1;
> }
> }
I think it all becomes simpler if you use only 2 bits. Such that:
bit0 is the prev R (0) or N (1) value,
bit1 is the next R (0) or N (1) value.
I think this should work because we don't care about the empty set
(currently 0000) and all the complexity in patch 5 is because we can
have R bits set when there's also N bits. The concequence of that is
that we cannot replace ! with ~ (which is what I kept doing).
But with only 2 bits, we only track the strongest relation in the set,
which is exactly what we appear to need.
The above then becomes something like:
static inline u8 __calc_dep(struct held_lock *lock)
{
return lock->read != 2;
}
static inline u8
calc_dep(struct held_lock *prev, struct held_lock *next)
{
return (__calc_dep(prev) << 0) | (__calc_dep(next) << 1);
}
entry->dep |= calc_dep(prev, next);
Then the stuff from 5 can be:
static inline bool is_rx(u8 dep)
{
return !(dep & 1);
}
static inline bool is_xr(u8 dep)
{
return !(dep & 2);
}
if (have_xr && is_rx(entry->dep))
continue;
entry->have_xr = is_xr(entry->dep);
Or did I mess that up somewhere?
next prev parent reply other threads:[~2018-02-23 11:55 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-22 7:08 [RFC tip/locking/lockdep v5 00/17] lockdep: Support deadlock detection for recursive read locks Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 01/17] lockdep: Demagic the return value of BFS Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 02/17] lockdep: Make __bfs() visit every dependency until a match Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 03/17] lockdep: Redefine LOCK_*_STATE* bits Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 04/17] lockdep: Introduce lock_list::dep Boqun Feng
2018-02-23 11:55 ` Peter Zijlstra [this message]
2018-02-23 12:37 ` Boqun Feng
2018-02-24 5:32 ` Boqun Feng
2018-02-24 6:30 ` Boqun Feng
2018-02-24 8:38 ` Peter Zijlstra
2018-02-24 9:00 ` Boqun Feng
2018-02-24 9:26 ` Boqun Feng
2018-02-26 9:00 ` Peter Zijlstra
2018-02-26 10:15 ` Boqun Feng
2018-02-26 10:20 ` Boqun Feng
2018-02-24 7:31 ` Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 05/17] lockdep: Extend __bfs() to work with multiple kinds of dependencies Boqun Feng
2018-02-22 14:26 ` Peter Zijlstra
2018-02-22 15:12 ` Boqun Feng
2018-02-22 15:30 ` Peter Zijlstra
2018-02-22 15:51 ` Peter Zijlstra
2018-02-22 16:31 ` Boqun Feng
2018-02-23 5:02 ` Boqun Feng
2018-02-23 11:15 ` Peter Zijlstra
2018-02-22 16:08 ` Peter Zijlstra
2018-02-22 16:34 ` Boqun Feng
2018-02-22 16:32 ` Peter Zijlstra
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular() Boqun Feng
2018-02-22 14:54 ` Peter Zijlstra
2018-02-22 15:16 ` Peter Zijlstra
2018-02-22 15:44 ` Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 07/17] lockdep: Adjust check_redundant() for recursive read change Boqun Feng
2018-02-22 17:29 ` Peter Zijlstra
2018-03-16 8:20 ` Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 08/17] lockdep: Fix recursive read lock related safe->unsafe detection Boqun Feng
2018-02-22 17:41 ` Peter Zijlstra
2018-02-22 17:46 ` Peter Zijlstra
2018-02-23 8:21 ` Boqun Feng
2018-02-23 8:58 ` Boqun Feng
2018-02-23 11:36 ` Peter Zijlstra
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 09/17] lockdep: Add recursive read locks into dependency graph Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 10/17] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 11/17] lockdep: Take read/write status in consideration when generate chainkey Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 12/17] lockdep/selftest: Unleash irq_read_recursion2 and add more Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 13/17] lockdep/selftest: Add more recursive read related test cases Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 14/17] Revert "locking/lockdep/selftests: Fix mixed read-write ABBA tests" Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 15/17] lockdep: Reduce the size of lock_list Boqun Feng
2018-02-23 11:38 ` Peter Zijlstra
2018-02-23 12:40 ` Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 16/17] lockdep: Documention for recursive read lock detection reasoning Boqun Feng
2018-02-24 22:53 ` Andrea Parri
2018-02-27 2:32 ` Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 17/17] MAINTAINERS: Add myself as a LOCKING PRIMITIVES reviewer Boqun Feng
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