From: Boqun Feng <boqun.feng@gmail.com>
To: Yuyang Du <duyuyang@gmail.com>
Cc: peterz@infradead.org, will.deacon@arm.com, mingo@kernel.org,
bvanassche@acm.org, ming.lei@redhat.com, frederic@kernel.org,
tglx@linutronix.de, paulmck@linux.ibm.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 02/17] locking/lockdep: Add read-write type for dependency
Date: Wed, 29 May 2019 19:37:45 +0800 [thread overview]
Message-ID: <20190529112321.GB5929@tardis> (raw)
In-Reply-To: <20190516080015.16033-3-duyuyang@gmail.com>
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On Thu, May 16, 2019 at 04:00:00PM +0800, Yuyang Du wrote:
> Direct dependency needs to keep track of its locks' read-write types. A
> union field is added to lock_list struct so the type is stored there as
> this:
>
> lock_type[1] (u16), lock_type[0] (u16)
>
> or:
>
> dep_type (int)
>
> where value:
>
> 0: exclusive / write
> 1: read
> 2: recursive read
>
> Note that (int) dep_type value may vary with different architectural
> endianness, so use helper functions to operate on these types.
>
> Signed-off-by: Yuyang Du <duyuyang@gmail.com>
> ---
> include/linux/lockdep.h | 12 ++++++++++++
> kernel/locking/lockdep.c | 34 +++++++++++++++++++++++++++++++---
> kernel/locking/lockdep_internals.h | 3 +++
> 3 files changed, 46 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 1009c47..bc09c85 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -195,6 +195,18 @@ struct lock_list {
> struct lock_class *links_to;
> struct lock_trace trace;
> int distance;
> + /*
> + * This field keeps track of the read-write type of this dependency.
> + *
> + * With L1 -> L2:
> + *
> + * lock_type[0] stores the type of L1, while lock_type[1] stores the
> + * type of L2.
> + */
> + union {
> + int dep_type;
> + u16 lock_type[2];
This takes extra space for storing the type of dependencies. In my
previous patchset, only 2bits are used, because you only need to care
about four types of dependencies:
1. Exclusive -> Recursive
2. Shared (read or recursive read) -> Recursive
3. Exclusize -> Non-Recursive (write or non-recursive readers)
4. Shared (read or recursive read) -> Non-Recursive
To understand why, here are my slides for Linux Plumber Conference last
year:
https://www.linuxplumbersconf.org/event/2/contributions/74/attachments/67/78/Recursive_read_deadlocks_and_Where_to_find_them.pdf
And we can steal two bits from "distance", since 2^30 would be enough.
I think it's important to save the size of lock_list since we will have
a lot of them.
Regards,
Boqun
> + };
>
> /*
> * The parent field is used to implement breadth-first search, and the
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index fb6be63..e7eedbf 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -1225,7 +1225,7 @@ static struct lock_list *alloc_list_entry(void)
> static int add_lock_to_list(struct lock_class *this,
> struct lock_class *links_to, struct list_head *head,
> unsigned long ip, int distance,
> - struct lock_trace *trace)
> + struct lock_trace *trace, int dep_type)
> {
> struct lock_list *entry;
> /*
> @@ -1240,6 +1240,8 @@ static int add_lock_to_list(struct lock_class *this,
> entry->links_to = links_to;
> entry->distance = distance;
> entry->trace = *trace;
> + entry->dep_type = dep_type;
> +
> /*
> * Both allocation and removal are done under the graph lock; but
> * iteration is under RCU-sched; see look_up_lock_class() and
> @@ -1677,6 +1679,30 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
> return ret;
> }
>
> +static inline int get_dep_type(struct held_lock *lock1, struct held_lock *lock2)
> +{
> + /*
> + * With dependency lock1 -> lock2:
> + *
> + * lock_type[0] is lock1, while lock_type[1] is lock2.
> + *
> + * Avoid architectural endianness difference composing dep_type.
> + */
> + u16 type[2] = { lock1->read, lock2->read };
> +
> + return *(int *)type;
> +}
> +
> +static inline int get_lock_type1(struct lock_list *lock)
> +{
> + return lock->lock_type[0];
> +}
> +
> +static inline int get_lock_type2(struct lock_list *lock)
> +{
> + return lock->lock_type[1];
> +}
> +
> /*
> * Check that the dependency graph starting at <src> can lead to
> * <target> or not. Print an error and return 0 if it does.
> @@ -2446,14 +2472,16 @@ static inline void inc_chains(void)
> */
> ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
> &hlock_class(prev)->locks_after,
> - next->acquire_ip, distance, trace);
> + next->acquire_ip, distance, trace,
> + get_dep_type(prev, next));
>
> if (!ret)
> return 0;
>
> ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
> &hlock_class(next)->locks_before,
> - next->acquire_ip, distance, trace);
> + next->acquire_ip, distance, trace,
> + get_dep_type(next, prev));
> if (!ret)
> return 0;
>
> diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
> index 150ec3f..c287bcb 100644
> --- a/kernel/locking/lockdep_internals.h
> +++ b/kernel/locking/lockdep_internals.h
> @@ -26,6 +26,9 @@ enum lock_usage_bit {
> #define LOCK_USAGE_DIR_MASK 2
> #define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK))
>
> +#define LOCK_TYPE_BITS 16
> +#define LOCK_TYPE_MASK 0xFFFF
> +
> /*
> * Usage-state bitmasks:
> */
> --
> 1.8.3.1
>
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next prev parent reply other threads:[~2019-05-29 11:37 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-16 7:59 [PATCH v2 00/17] Support for read-write lock deadlock detection Yuyang Du
2019-05-16 7:59 ` [PATCH v2 01/17] locking/lockdep: Add lock type enum to explicitly specify read or write locks Yuyang Du
2019-05-16 8:00 ` [PATCH v2 02/17] locking/lockdep: Add read-write type for dependency Yuyang Du
2019-05-29 11:37 ` Boqun Feng [this message]
2019-05-16 8:00 ` [PATCH v2 03/17] locking/lockdep: Add helper functions to operate on the searched path Yuyang Du
2019-05-16 8:00 ` [PATCH v2 04/17] locking/lockdep: Update direct dependency's read-write type if it exists Yuyang Du
2019-05-16 8:00 ` [PATCH v2 05/17] locking/lockdep: Rename deadlock check functions Yuyang Du
2019-05-16 8:00 ` [PATCH v2 06/17] locking/lockdep: Adjust BFS algorithm to support multiple matches Yuyang Du
2019-05-16 8:00 ` [PATCH v2 07/17] locking/lockdep: Introduce mark_lock_unaccessed() Yuyang Du
2019-05-16 8:00 ` [PATCH v2 08/17] locking/lockdep: Introduce chain_hlocks_type for held lock's read-write type Yuyang Du
2019-05-16 8:00 ` [PATCH v2 09/17] locking/lockdep: Hash held lock's read-write type into chain key Yuyang Du
2019-05-16 8:00 ` [PATCH v2 10/17] locking/lockdep: Support read-write lock's deadlock detection Yuyang Du
2019-05-16 8:00 ` [PATCH v2 11/17] locking/lockdep: Adjust lockdep selftest cases Yuyang Du
2019-05-29 11:44 ` Boqun Feng
2019-05-30 7:37 ` Yuyang Du
2019-05-16 8:00 ` [PATCH v2 12/17] locking/lockdep: Remove useless lock type assignment Yuyang Du
2019-05-16 8:00 ` [PATCH v2 13/17] locking/lockdep: Add nest lock type Yuyang Du
2019-05-16 8:00 ` [PATCH v2 14/17] locking/lockdep: Support recursive read locks Yuyang Du
2019-05-16 8:00 ` [PATCH v2 15/17] locking/lockdep: Adjust selftest case for recursive read lock Yuyang Du
2019-05-16 8:00 ` [PATCH v2 16/17] locking/lockdep: Add more lockdep selftest cases Yuyang Du
2019-05-16 8:00 ` [PATCH v2 17/17] locking/lockdep: Remove irq-safe to irq-unsafe read check Yuyang Du
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