udldrmfb: Fix EDID not working with monitors with EDID extension blocks

[~andy/linux] / lib / percpu-rwsem.c

diff --git a/lib/percpu-rwsem.c b/lib/percpu-rwsem.c
index 2e03bcfe48f918e82acb762f32a52e3c0b0a9dbb..652a8ee8efe95acaf1db28eeed40bba820787222 100644 (file)
--- a/lib/percpu-rwsem.c
+++ b/lib/percpu-rwsem.c
@@ -1,20 +1,23 @@
-#include <linux/mutex.h>
+#include <linux/atomic.h>
 #include <linux/rwsem.h>
 #include <linux/percpu.h>
 #include <linux/wait.h>
+#include <linux/lockdep.h>
 #include <linux/percpu-rwsem.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 #include <linux/errno.h>
 
-int percpu_init_rwsem(struct percpu_rw_semaphore *brw)
+int __percpu_init_rwsem(struct percpu_rw_semaphore *brw,
+                       const char *name, struct lock_class_key *rwsem_key)
 {
        brw->fast_read_ctr = alloc_percpu(int);
        if (unlikely(!brw->fast_read_ctr))
                return -ENOMEM;
 
-       mutex_init(&brw->writer_mutex);
-       init_rwsem(&brw->rw_sem);
+       /* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
+       __init_rwsem(&brw->rw_sem, name, rwsem_key);
+       atomic_set(&brw->write_ctr, 0);
        atomic_set(&brw->slow_read_ctr, 0);
        init_waitqueue_head(&brw->write_waitq);
        return 0;
@@ -28,7 +31,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
 
 /*
  * This is the fast-path for down_read/up_read, it only needs to ensure
- * there is no pending writer (!mutex_is_locked() check) and inc/dec the
+ * there is no pending writer (atomic_read(write_ctr) == 0) and inc/dec the
  * fast per-cpu counter. The writer uses synchronize_sched_expedited() to
  * serialize with the preempt-disabled section below.
  *
@@ -44,7 +47,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
  * If this helper fails the callers rely on the normal rw_semaphore and
  * atomic_dec_and_test(), so in this case we have the necessary barriers.
  *
- * But if it succeeds we do not have any barriers, mutex_is_locked() or
+ * But if it succeeds we do not have any barriers, atomic_read(write_ctr) or
  * __this_cpu_add() below can be reordered with any LOAD/STORE done by the
  * reader inside the critical section. See the comments in down_write and
  * up_write below.
@@ -54,7 +57,7 @@ static bool update_fast_ctr(struct percpu_rw_semaphore *brw, unsigned int val)
        bool success = false;
 
        preempt_disable();
-       if (likely(!mutex_is_locked(&brw->writer_mutex))) {
+       if (likely(!atomic_read(&brw->write_ctr))) {
                __this_cpu_add(*brw->fast_read_ctr, val);
                success = true;
        }
@@ -66,19 +69,29 @@ static bool update_fast_ctr(struct percpu_rw_semaphore *brw, unsigned int val)
 /*
  * Like the normal down_read() this is not recursive, the writer can
  * come after the first percpu_down_read() and create the deadlock.
+ *
+ * Note: returns with lock_is_held(brw->rw_sem) == T for lockdep,
+ * percpu_up_read() does rwsem_release(). This pairs with the usage
+ * of ->rw_sem in percpu_down/up_write().
  */
 void percpu_down_read(struct percpu_rw_semaphore *brw)
 {
-       if (likely(update_fast_ctr(brw, +1)))
+       might_sleep();
+       if (likely(update_fast_ctr(brw, +1))) {
+               rwsem_acquire_read(&brw->rw_sem.dep_map, 0, 0, _RET_IP_);
                return;
+       }
 
        down_read(&brw->rw_sem);
        atomic_inc(&brw->slow_read_ctr);
-       up_read(&brw->rw_sem);
+       /* avoid up_read()->rwsem_release() */
+       __up_read(&brw->rw_sem);
 }
 
 void percpu_up_read(struct percpu_rw_semaphore *brw)
 {
+       rwsem_release(&brw->rw_sem.dep_map, 1, _RET_IP_);
+
        if (likely(update_fast_ctr(brw, -1)))
                return;
 
@@ -101,9 +114,8 @@ static int clear_fast_ctr(struct percpu_rw_semaphore *brw)
 }
 
 /*
- * A writer takes ->writer_mutex to exclude other writers and to force the
- * readers to switch to the slow mode, note the mutex_is_locked() check in
- * update_fast_ctr().
+ * A writer increments ->write_ctr to force the readers to switch to the
+ * slow mode, note the atomic_read() check in update_fast_ctr().
  *
  * After that the readers can only inc/dec the slow ->slow_read_ctr counter,
  * ->fast_read_ctr is stable. Once the writer moves its sum into the slow
@@ -114,11 +126,10 @@ static int clear_fast_ctr(struct percpu_rw_semaphore *brw)
  */
 void percpu_down_write(struct percpu_rw_semaphore *brw)
 {
-       /* also blocks update_fast_ctr() which checks mutex_is_locked() */
-       mutex_lock(&brw->writer_mutex);
-
+       /* tell update_fast_ctr() there is a pending writer */
+       atomic_inc(&brw->write_ctr);
        /*
-        * 1. Ensures mutex_is_locked() is visible to any down_read/up_read
+        * 1. Ensures that write_ctr != 0 is visible to any down_read/up_read
         *    so that update_fast_ctr() can't succeed.
         *
         * 2. Ensures we see the result of every previous this_cpu_add() in
@@ -130,25 +141,25 @@ void percpu_down_write(struct percpu_rw_semaphore *brw)
         */
        synchronize_sched_expedited();
 
+       /* exclude other writers, and block the new readers completely */
+       down_write(&brw->rw_sem);
+
        /* nobody can use fast_read_ctr, move its sum into slow_read_ctr */
        atomic_add(clear_fast_ctr(brw), &brw->slow_read_ctr);
 
-       /* block the new readers completely */
-       down_write(&brw->rw_sem);
-
        /* wait for all readers to complete their percpu_up_read() */
        wait_event(brw->write_waitq, !atomic_read(&brw->slow_read_ctr));
 }
 
 void percpu_up_write(struct percpu_rw_semaphore *brw)
 {
-       /* allow the new readers, but only the slow-path */
+       /* release the lock, but the readers can't use the fast-path */
        up_write(&brw->rw_sem);
-
        /*
         * Insert the barrier before the next fast-path in down_read,
         * see W_R case in the comment above update_fast_ctr().
         */
        synchronize_sched_expedited();
-       mutex_unlock(&brw->writer_mutex);
+       /* the last writer unblocks update_fast_ctr() */
+       atomic_dec(&brw->write_ctr);
 }