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authorPeter Zijlstra <peterz@infradead.org>2014-09-30 15:26:00 +0200
committerIngo Molnar <mingo@kernel.org>2014-10-03 06:09:30 +0200
commit8acd91e8620836a56ff62028ed28ba629f2881a0 (patch)
tree4a95b0d1a41b75f6ad4cd8a6c59dcdb9268d1e4b
parentdebfab74e453f079cd8b12b0604387a8c510ef3a (diff)
locking/lockdep: Revert qrwlock recusive stuff
Commit f0bab73cb539 ("locking/lockdep: Restrict the use of recursive read_lock() with qrwlock") changed lockdep to try and conform to the qrwlock semantics which differ from the traditional rwlock semantics. In particular qrwlock is fair outside of interrupt context, but in interrupt context readers will ignore all fairness. The problem modeling this is that read and write side have different lock state (interrupts) semantics but we only have a single representation of these. Therefore lockdep will get confused, thinking the lock can cause interrupt lock inversions. So revert it for now; the old rwlock semantics were already imperfectly modeled and the qrwlock extra won't fit either. If we want to properly fix this, I think we need to resurrect the work by Gautham did a few years ago that split the read and write state of locks: http://lwn.net/Articles/332801/ FWIW the locking selftest that would've failed (and was reported by Borislav earlier) is something like: RL(X1); /* IRQ-ON */ LOCK(A); UNLOCK(A); RU(X1); IRQ_ENTER(); RL(X1); /* IN-IRQ */ RU(X1); IRQ_EXIT(); At which point it would report that because A is an IRQ-unsafe lock we can suffer the following inversion: CPU0 CPU1 lock(A) lock(X1) lock(A) <IRQ> lock(X1) And this is 'wrong' because X1 can recurse (assuming the above lock are in fact read-lock) but lockdep doesn't know about this. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Waiman Long <Waiman.Long@hp.com> Cc: ego@linux.vnet.ibm.com Cc: bp@alien8.de Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20140930132600.GA7444@worktop.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--include/linux/lockdep.h10
-rw-r--r--kernel/locking/lockdep.c6
-rw-r--r--lib/locking-selftest.c56
3 files changed, 8 insertions, 64 deletions
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b5a84b62fb84..f388481201cd 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -478,24 +478,16 @@ 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_irecursive(l, s, t, NULL, i)
+#define rwlock_acquire_read(l, s, t, i) lock_acquire_shared_recursive(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 420ba685c4e5..88d0d4420ad2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3597,12 +3597,6 @@ 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,
diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 62af709b2083..872a15a2a637 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -267,46 +267,19 @@ GENERATE_TESTCASE(AA_rsem)
#undef E
/*
- * Special-case for read-locking, they are not allowed to
- * recurse on the same lock class except under interrupt context:
+ * Special-case for read-locking, they are
+ * allowed to recurse on the same lock class:
*/
static void rlock_AA1(void)
{
RL(X1);
- RL(X1); // this one should fail
+ RL(X1); // this one should NOT fail
}
static void rlock_AA1B(void)
{
RL(X1);
- RL(X2); // this one should fail
-}
-
-static void rlock_AHA1(void)
-{
- RL(X1);
- HARDIRQ_ENTER();
- RL(X1); // this one should NOT fail
- HARDIRQ_EXIT();
-}
-
-static void rlock_AHA1B(void)
-{
- RL(X1);
- HARDIRQ_ENTER();
- RL(X2); // this one should NOT fail
- HARDIRQ_EXIT();
-}
-
-static void rlock_ASAHA1(void)
-{
- RL(X1);
- SOFTIRQ_ENTER();
- RL(X1); // this one should NOT fail
- HARDIRQ_ENTER();
- RL(X1); // this one should NOT fail
- HARDIRQ_EXIT();
- SOFTIRQ_EXIT();
+ RL(X2); // this one should NOT fail
}
static void rsem_AA1(void)
@@ -1096,7 +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, FAILURE, LOCKTYPE_RWLOCK); \
+ dotest(name##_rlock, SUCCESS, LOCKTYPE_RWLOCK); \
dotest(name##_mutex, FAILURE, LOCKTYPE_MUTEX); \
dotest(name##_wsem, FAILURE, LOCKTYPE_RWSEM); \
dotest(name##_rsem, FAILURE, LOCKTYPE_RWSEM); \
@@ -1857,14 +1830,14 @@ void locking_selftest(void)
printk(" --------------------------------------------------------------------------\n");
print_testname("recursive read-lock");
printk(" |");
- dotest(rlock_AA1, FAILURE, LOCKTYPE_RWLOCK);
+ dotest(rlock_AA1, SUCCESS, LOCKTYPE_RWLOCK);
printk(" |");
dotest(rsem_AA1, FAILURE, LOCKTYPE_RWSEM);
printk("\n");
print_testname("recursive read-lock #2");
printk(" |");
- dotest(rlock_AA1B, FAILURE, LOCKTYPE_RWLOCK);
+ dotest(rlock_AA1B, SUCCESS, LOCKTYPE_RWLOCK);
printk(" |");
dotest(rsem_AA1B, FAILURE, LOCKTYPE_RWSEM);
printk("\n");
@@ -1883,21 +1856,6 @@ void locking_selftest(void)
dotest(rsem_AA3, FAILURE, LOCKTYPE_RWSEM);
printk("\n");
- print_testname("recursive rlock with interrupt");
- printk(" |");
- dotest(rlock_AHA1, SUCCESS, LOCKTYPE_RWLOCK);
- printk("\n");
-
- print_testname("recursive rlock with interrupt #2");
- printk(" |");
- dotest(rlock_AHA1B, SUCCESS, LOCKTYPE_RWLOCK);
- printk("\n");
-
- print_testname("recursive rlock with interrupt #3");
- printk(" |");
- dotest(rlock_ASAHA1, SUCCESS, LOCKTYPE_RWLOCK);
- printk("\n");
-
printk(" --------------------------------------------------------------------------\n");
/*

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