From: Yuyang Du <duyuyang@gmail.com>
To: peterz@infradead.org, will.deacon@arm.com, mingo@kernel.org
Cc: bvanassche@acm.org, ming.lei@redhat.com, frederic@kernel.org,
tglx@linutronix.de, boqun.feng@gmail.com, paulmck@linux.ibm.com,
linux-kernel@vger.kernel.org, Yuyang Du <duyuyang@gmail.com>
Subject: [PATCH v2 17/17] locking/lockdep: Remove irq-safe to irq-unsafe read check
Date: Thu, 16 May 2019 16:00:15 +0800 [thread overview]
Message-ID: <20190516080015.16033-18-duyuyang@gmail.com> (raw)
In-Reply-To: <20190516080015.16033-1-duyuyang@gmail.com>
We have a lockdep warning:
========================================================
WARNING: possible irq lock inversion dependency detected
5.1.0-rc7+ #141 Not tainted
--------------------------------------------------------
kworker/8:2/328 just changed the state of lock:
0000000007f1a95b (&(&host->lock)->rlock){-...}, at: ata_bmdma_interrupt+0x27/0x1c0 [libata]
but this lock took another, HARDIRQ-READ-unsafe lock in the past:
(&trig->leddev_list_lock){.+.?}
and interrupts could create inverse lock ordering between them.
other info that might help us debug this:
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&trig->leddev_list_lock);
local_irq_disable();
lock(&(&host->lock)->rlock);
lock(&trig->leddev_list_lock);
<Interrupt>
lock(&(&host->lock)->rlock);
*** DEADLOCK ***
This splat is a false positive, which is enabled by the addition of
recursive read locks in the graph. Specifically, trig->leddev_list_lock is a
rwlock_t type, which was not in the graph before recursive read lock support
was added in lockdep.
This false positve is caused by a "false-positive" check in IRQ usage check.
In mark_lock_irq(), the following checks are currently performed:
----------------------------------
| -> | unsafe | read unsafe |
|----------------------------------|
| safe | F B | F* B* |
|----------------------------------|
| read safe | F* B* | - |
----------------------------------
Where:
F: check_usage_forwards
B: check_usage_backwards
*: check enabled by STRICT_READ_CHECKS
But actually the safe -> unsafe read dependency does not create a deadlock
scenario.
Fix this by simply removing those two checks, and since safe read -> unsafe
is indeed a problem, these checks are not actually strict per se, so remove
the macro STRICT_READ_CHECKS, and we have the following checks:
----------------------------------
| -> | unsafe | read unsafe |
|----------------------------------|
| safe | F B | - |
|----------------------------------|
| read safe | F B | - |
----------------------------------
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
kernel/locking/lockdep.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index cd1d515..bc36fbf 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3450,8 +3450,6 @@ static int SOFTIRQ_verbose(struct lock_class *class)
return 0;
}
-#define STRICT_READ_CHECKS 1
-
static int (*state_verbose_f[])(struct lock_class *class) = {
#define LOCKDEP_STATE(__STATE) \
__STATE##_verbose,
@@ -3497,7 +3495,7 @@ typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
* Validate that the lock dependencies don't have conflicting usage
* states.
*/
- if ((!read || STRICT_READ_CHECKS) &&
+ if ((!read || !dir) &&
!usage(curr, this, excl_bit, state_name(new_bit & ~LOCK_USAGE_READ_MASK)))
return 0;
@@ -3508,7 +3506,7 @@ typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
if (!valid_state(curr, this, new_bit, excl_bit + LOCK_USAGE_READ_MASK))
return 0;
- if (STRICT_READ_CHECKS &&
+ if (dir &&
!usage(curr, this, excl_bit + LOCK_USAGE_READ_MASK,
state_name(new_bit + LOCK_USAGE_READ_MASK)))
return 0;
--
1.8.3.1
prev parent reply other threads:[~2019-05-16 8:01 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
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 ` Yuyang Du [this message]
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