obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o
obj-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
-obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem-xadd.o
\ No newline at end of file
+obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem-xadd.o
+obj-$(CONFIG_PERCPU_RWSEM) += percpu-rwsem.o
--- /dev/null
+#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,
+ const char *name, struct lock_class_key *rwsem_key)
+{
+ brw->fast_read_ctr = alloc_percpu(int);
+ if (unlikely(!brw->fast_read_ctr))
+ return -ENOMEM;
+
+ /* ->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;
+}
+
+void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
+{
+ free_percpu(brw->fast_read_ctr);
+ brw->fast_read_ctr = NULL; /* catch use after free bugs */
+}
+
+/*
+ * This is the fast-path for down_read/up_read, it only needs to ensure
+ * 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.
+ *
+ * The nontrivial part is that we should guarantee acquire/release semantics
+ * in case when
+ *
+ * R_W: down_write() comes after up_read(), the writer should see all
+ * changes done by the reader
+ * or
+ * W_R: down_read() comes after up_write(), the reader should see all
+ * changes done by the writer
+ *
+ * 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, 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.
+ */
+static bool update_fast_ctr(struct percpu_rw_semaphore *brw, unsigned int val)
+{
+ bool success = false;
+
+ preempt_disable();
+ if (likely(!atomic_read(&brw->write_ctr))) {
+ __this_cpu_add(*brw->fast_read_ctr, val);
+ success = true;
+ }
+ preempt_enable();
+
+ return success;
+}
+
+/*
+ * 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)
+{
+ 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);
+ /* 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;
+
+ /* false-positive is possible but harmless */
+ if (atomic_dec_and_test(&brw->slow_read_ctr))
+ wake_up_all(&brw->write_waitq);
+}
+
+static int clear_fast_ctr(struct percpu_rw_semaphore *brw)
+{
+ unsigned int sum = 0;
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ sum += per_cpu(*brw->fast_read_ctr, cpu);
+ per_cpu(*brw->fast_read_ctr, cpu) = 0;
+ }
+
+ return sum;
+}
+
+/*
+ * 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
+ * counter it represents the number of active readers.
+ *
+ * Finally the writer takes ->rw_sem for writing and blocks the new readers,
+ * then waits until the slow counter becomes zero.
+ */
+void percpu_down_write(struct percpu_rw_semaphore *brw)
+{
+ /* tell update_fast_ctr() there is a pending writer */
+ atomic_inc(&brw->write_ctr);
+ /*
+ * 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
+ * update_fast_ctr().
+ *
+ * 3. Ensures that if any reader has exited its critical section via
+ * fast-path, it executes a full memory barrier before we return.
+ * See R_W case in the comment above update_fast_ctr().
+ */
+ 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);
+
+ /* 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)
+{
+ /* 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();
+ /* the last writer unblocks update_fast_ctr() */
+ atomic_dec(&brw->write_ctr);
+}
obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o
obj-$(CONFIG_CHECK_SIGNATURE) += check_signature.o
obj-$(CONFIG_DEBUG_LOCKING_API_SELFTESTS) += locking-selftest.o
-lib-$(CONFIG_PERCPU_RWSEM) += percpu-rwsem.o
CFLAGS_hweight.o = $(subst $(quote),,$(CONFIG_ARCH_HWEIGHT_CFLAGS))
obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
+++ /dev/null
-#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,
- const char *name, struct lock_class_key *rwsem_key)
-{
- brw->fast_read_ctr = alloc_percpu(int);
- if (unlikely(!brw->fast_read_ctr))
- return -ENOMEM;
-
- /* ->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;
-}
-
-void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
-{
- free_percpu(brw->fast_read_ctr);
- brw->fast_read_ctr = NULL; /* catch use after free bugs */
-}
-
-/*
- * This is the fast-path for down_read/up_read, it only needs to ensure
- * 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.
- *
- * The nontrivial part is that we should guarantee acquire/release semantics
- * in case when
- *
- * R_W: down_write() comes after up_read(), the writer should see all
- * changes done by the reader
- * or
- * W_R: down_read() comes after up_write(), the reader should see all
- * changes done by the writer
- *
- * 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, 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.
- */
-static bool update_fast_ctr(struct percpu_rw_semaphore *brw, unsigned int val)
-{
- bool success = false;
-
- preempt_disable();
- if (likely(!atomic_read(&brw->write_ctr))) {
- __this_cpu_add(*brw->fast_read_ctr, val);
- success = true;
- }
- preempt_enable();
-
- return success;
-}
-
-/*
- * 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)
-{
- 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);
- /* 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;
-
- /* false-positive is possible but harmless */
- if (atomic_dec_and_test(&brw->slow_read_ctr))
- wake_up_all(&brw->write_waitq);
-}
-
-static int clear_fast_ctr(struct percpu_rw_semaphore *brw)
-{
- unsigned int sum = 0;
- int cpu;
-
- for_each_possible_cpu(cpu) {
- sum += per_cpu(*brw->fast_read_ctr, cpu);
- per_cpu(*brw->fast_read_ctr, cpu) = 0;
- }
-
- return sum;
-}
-
-/*
- * 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
- * counter it represents the number of active readers.
- *
- * Finally the writer takes ->rw_sem for writing and blocks the new readers,
- * then waits until the slow counter becomes zero.
- */
-void percpu_down_write(struct percpu_rw_semaphore *brw)
-{
- /* tell update_fast_ctr() there is a pending writer */
- atomic_inc(&brw->write_ctr);
- /*
- * 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
- * update_fast_ctr().
- *
- * 3. Ensures that if any reader has exited its critical section via
- * fast-path, it executes a full memory barrier before we return.
- * See R_W case in the comment above update_fast_ctr().
- */
- 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);
-
- /* 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)
-{
- /* 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();
- /* the last writer unblocks update_fast_ctr() */
- atomic_dec(&brw->write_ctr);
-}
projects / mirror_ubuntu-zesty-kernel.git / commitdiff