v5->v6:
- Unconditionally disallow the use of recursive read-lock in process
context.
- Promote read state 3 to 2 when in interrupt context instead of
doing additional check in check_deadlock().
- Fix some comments in locking-selftest.c.
v4->v5:
- Add patch 2 to update the locking selftest code to handle recursive
read_lock correctly. Patch 1 has no change.
v3->v4:
- Document the new read state and move the conditional compilation code
to lockdep.h.
v2->v3:
- Add a new read mode (3) for rwlock (used in
lock_acquire_shared_cond_recursive()) to avoid conflict with other
use cases of lock_acquire_shared_recursive().
v1->v2:
- Use less conditional & make it easier to read
With the merging of qrwlock into 3.16, it was found that the btrfs
filesystem hanged readily. A fix was devised and merged into rc2 and
the use of recursive read_lock call was part of the problem.
This patch series addes code to the lockdep subsystem to catch this
kind of recursive read_lock calls in kernel code. It also updates
the locking selftest to handle recursive read_lock correctly so that
it won't complain about test failures.
Waiman Long (2):
locking/lockdep: Restrict the use of recursive read_lock() with
qrwlock
locking/selftest: Support queued rwlock
include/linux/lockdep.h | 10 +++++++++-
kernel/locking/lockdep.c | 6 ++++++
lib/locking-selftest.c | 12 ++++++------
3 files changed, 21 insertions(+), 7 deletions(-)
Unlike the original unfair rwlock implementation, queued rwlock
will grant lock according to the chronological sequence of the lock
requests except when the lock requester is in the interrupt context.
Consequently, recursive read_lock calls will now hang the process if
there is a write_lock call somewhere in between the read_lock calls.
This patch updates the lockdep implementation to look for recursive
read_lock calls. A new read state (3) is used to mark those read_lock
call that cannot be recursively called except in the interrupt
context. The new read state does exhaust the 2 bits available in
held_lock:read bit field. The addition of any new read state in the
future may require a redesign of how all those bits are squeezed
together in the held_lock structure.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
---
include/linux/lockdep.h | 10 +++++++++-
kernel/locking/lockdep.c | 6 ++++++
2 files changed, 15 insertions(+), 1 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 008388f..dadd6ba 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -478,16 +478,24 @@ static inline void print_irqtrace_events(struct task_struct *curr)
* on the per lock-class debug mode:
*/
+/*
+ * Read states in the 2-bit held_lock:read field:
+ * 0: Exclusive lock
+ * 1: Shareable lock, cannot be recursively called
+ * 2: Shareable lock, can be recursively called
+ * 3: Shareable lock, cannot be recursively called except in interrupt context
+ */
#define lock_acquire_exclusive(l, s, t, n, i) lock_acquire(l, s, t, 0, 1, n, i)
#define lock_acquire_shared(l, s, t, n, i) lock_acquire(l, s, t, 1, 1, n, i)
#define lock_acquire_shared_recursive(l, s, t, n, i) lock_acquire(l, s, t, 2, 1, n, i)
+#define lock_acquire_shared_irecursive(l, s, t, n, i) lock_acquire(l, s, t, 3, 1, n, i)
#define spin_acquire(l, s, t, i) lock_acquire_exclusive(l, s, t, NULL, i)
#define spin_acquire_nest(l, s, t, n, i) lock_acquire_exclusive(l, s, t, n, i)
#define spin_release(l, n, i) lock_release(l, n, i)
#define rwlock_acquire(l, s, t, i) lock_acquire_exclusive(l, s, t, NULL, i)
-#define rwlock_acquire_read(l, s, t, i) lock_acquire_shared_recursive(l, s, t, NULL, i)
+#define rwlock_acquire_read(l, s, t, i) lock_acquire_shared_irecursive(l, s, t, NULL, i)
#define rwlock_release(l, n, i) lock_release(l, n, i)
#define seqcount_acquire(l, s, t, i) lock_acquire_exclusive(l, s, t, NULL, i)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index d24e433..097f8ad 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3595,6 +3595,12 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
raw_local_irq_save(flags);
check_flags(flags);
+ /*
+ * An interrupt recursive read in interrupt context can be considered
+ * to be the same as a recursive read from checking perspective.
+ */
+ if ((read == 3) && in_interrupt())
+ read = 2;
current->lockdep_recursion = 1;
trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
__lock_acquire(lock, subclass, trylock, read, check,
--
1.7.1
The queued rwlock does not support the use of recursive read-lock in
the process context. With changes in the lockdep code to check and
disallow recursive read-lock, it is also necessary for the locking
selftest to be updated to change the process context recursive read
locking results from SUCCESS to FAILURE for rwlock.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
---
lib/locking-selftest.c | 12 ++++++------
1 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 872a15a..9a33688 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -267,19 +267,19 @@ GENERATE_TESTCASE(AA_rsem)
#undef E
/*
- * Special-case for read-locking, they are
+ * Special-case for read-locking, they are not
* allowed to recurse on the same lock class:
*/
static void rlock_AA1(void)
{
RL(X1);
- RL(X1); // this one should NOT fail
+ RL(X1); // this one should fail
}
static void rlock_AA1B(void)
{
RL(X1);
- RL(X2); // this one should NOT fail
+ RL(X2); // this one should fail
}
static void rsem_AA1(void)
@@ -1069,7 +1069,7 @@ static inline void print_testname(const char *testname)
print_testname(desc); \
dotest(name##_spin, FAILURE, LOCKTYPE_SPIN); \
dotest(name##_wlock, FAILURE, LOCKTYPE_RWLOCK); \
- dotest(name##_rlock, SUCCESS, LOCKTYPE_RWLOCK); \
+ dotest(name##_rlock, FAILURE, LOCKTYPE_RWLOCK); \
dotest(name##_mutex, FAILURE, LOCKTYPE_MUTEX); \
dotest(name##_wsem, FAILURE, LOCKTYPE_RWSEM); \
dotest(name##_rsem, FAILURE, LOCKTYPE_RWSEM); \
@@ -1830,14 +1830,14 @@ void locking_selftest(void)
printk(" --------------------------------------------------------------------------\n");
print_testname("recursive read-lock");
printk(" |");
- dotest(rlock_AA1, SUCCESS, LOCKTYPE_RWLOCK);
+ dotest(rlock_AA1, FAILURE, LOCKTYPE_RWLOCK);
printk(" |");
dotest(rsem_AA1, FAILURE, LOCKTYPE_RWSEM);
printk("\n");
print_testname("recursive read-lock #2");
printk(" |");
- dotest(rlock_AA1B, SUCCESS, LOCKTYPE_RWLOCK);
+ dotest(rlock_AA1B, FAILURE, LOCKTYPE_RWLOCK);
printk(" |");
dotest(rsem_AA1B, FAILURE, LOCKTYPE_RWSEM);
printk("\n");
--
1.7.1