relay: Use per CPU constructs for the relay channel buffer pointers

relay essentially needs to maintain a per CPU array of channel buffer
pointers but it manually creates that array.  Instead its better to use
the per CPU constructs, provided by the kernel, to allocate & access the
array of pointer to channel buffers.

Signed-off-by: Akash Goel <akash.goel@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://lkml.kernel.org/r/1470909140-25919-1-git-send-email-akash.goel@intel.com
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/relay.h

@@ -19,6 +19,7 @@
 #include <linux/fs.h>
 #include <linux/poll.h>
 #include <linux/kref.h>
+#include <linux/percpu.h>
 
 /*
  * Tracks changes to rchan/rchan_buf structs
@@ -63,7 +64,7 @@ struct rchan
 	struct kref kref;		/* channel refcount */
 	void *private_data;		/* for user-defined data */
 	size_t last_toobig;		/* tried to log event > subbuf size */
-	struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
+	struct rchan_buf ** __percpu buf; /* per-cpu channel buffers */
 	int is_global;			/* One global buffer ? */
 	struct list_head list;		/* for channel list */
 	struct dentry *parent;		/* parent dentry passed to open */
@@ -204,7 +205,7 @@ static inline void relay_write(struct rchan *chan,
 	struct rchan_buf *buf;
 
 	local_irq_save(flags);
-	buf = chan->buf[smp_processor_id()];
+	buf = *this_cpu_ptr(chan->buf);
 	if (unlikely(buf->offset + length > chan->subbuf_size))
 		length = relay_switch_subbuf(buf, length);
 	memcpy(buf->data + buf->offset, data, length);
@@ -230,12 +231,12 @@ static inline void __relay_write(struct rchan *chan,
 {
 	struct rchan_buf *buf;
 
-	buf = chan->buf[get_cpu()];
+	buf = *get_cpu_ptr(chan->buf);
 	if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 		length = relay_switch_subbuf(buf, length);
 	memcpy(buf->data + buf->offset, data, length);
 	buf->offset += length;
-	put_cpu();
+	put_cpu_ptr(chan->buf);
 }
 
 /**
@@ -251,17 +252,19 @@ static inline void __relay_write(struct rchan *chan,
  */
 static inline void *relay_reserve(struct rchan *chan, size_t length)
 {
-	void *reserved;
-	struct rchan_buf *buf = chan->buf[smp_processor_id()];
+	void *reserved = NULL;
+	struct rchan_buf *buf = *get_cpu_ptr(chan->buf);
 
 	if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 		length = relay_switch_subbuf(buf, length);
 		if (!length)
-			return NULL;
+			goto end;
 	}
 	reserved = buf->data + buf->offset;
 	buf->offset += length;
 
+end:
+	put_cpu_ptr(chan->buf);
 	return reserved;
 }
 

kernel/relay.c

@@ -214,7 +214,7 @@ static void relay_destroy_buf(struct rchan_buf *buf)
 			__free_page(buf->page_array[i]);
 		relay_free_page_array(buf->page_array);
 	}
-	chan->buf[buf->cpu] = NULL;
+	*per_cpu_ptr(chan->buf, buf->cpu) = NULL;
 	kfree(buf->padding);
 	kfree(buf);
 	kref_put(&chan->kref, relay_destroy_channel);
@@ -382,20 +382,21 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
  */
 void relay_reset(struct rchan *chan)
 {
+	struct rchan_buf *buf;
 	unsigned int i;
 
 	if (!chan)
 		return;
 
-	if (chan->is_global && chan->buf[0]) {
-		__relay_reset(chan->buf[0], 0);
+	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
+		__relay_reset(buf, 0);
 		return;
 	}
 
 	mutex_lock(&relay_channels_mutex);
 	for_each_possible_cpu(i)
-		if (chan->buf[i])
-			__relay_reset(chan->buf[i], 0);
+		if ((buf = *per_cpu_ptr(chan->buf, i)))
+			__relay_reset(buf, 0);
 	mutex_unlock(&relay_channels_mutex);
 }
 EXPORT_SYMBOL_GPL(relay_reset);
@@ -440,7 +441,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
 	struct dentry *dentry;
 
  	if (chan->is_global)
-		return chan->buf[0];
+		return *per_cpu_ptr(chan->buf, 0);
 
 	buf = relay_create_buf(chan);
 	if (!buf)
@@ -464,7 +465,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
  	__relay_reset(buf, 1);
 
  	if(chan->is_global) {
- 		chan->buf[0] = buf;
+		*per_cpu_ptr(chan->buf, 0) = buf;
  		buf->cpu = 0;
   	}
 
@@ -526,22 +527,24 @@ static int relay_hotcpu_callback(struct notifier_block *nb,
 {
 	unsigned int hotcpu = (unsigned long)hcpu;
 	struct rchan *chan;
+	struct rchan_buf *buf;
 
 	switch(action) {
 	case CPU_UP_PREPARE:
 	case CPU_UP_PREPARE_FROZEN:
 		mutex_lock(&relay_channels_mutex);
 		list_for_each_entry(chan, &relay_channels, list) {
-			if (chan->buf[hotcpu])
+			if ((buf = *per_cpu_ptr(chan->buf, hotcpu)))
 				continue;
-			chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
-			if(!chan->buf[hotcpu]) {
+			buf = relay_open_buf(chan, hotcpu);
+			if (!buf) {
 				printk(KERN_ERR
 					"relay_hotcpu_callback: cpu %d buffer "
 					"creation failed\n", hotcpu);
 				mutex_unlock(&relay_channels_mutex);
 				return notifier_from_errno(-ENOMEM);
 			}
+			*per_cpu_ptr(chan->buf, hotcpu) = buf;
 		}
 		mutex_unlock(&relay_channels_mutex);
 		break;
@@ -583,6 +586,7 @@ struct rchan *relay_open(const char *base_filename,
 {
 	unsigned int i;
 	struct rchan *chan;
+	struct rchan_buf *buf;
 
 	if (!(subbuf_size && n_subbufs))
 		return NULL;
@@ -593,6 +597,7 @@ struct rchan *relay_open(const char *base_filename,
 	if (!chan)
 		return NULL;
 
+	chan->buf = alloc_percpu(struct rchan_buf *);
 	chan->version = RELAYFS_CHANNEL_VERSION;
 	chan->n_subbufs = n_subbufs;
 	chan->subbuf_size = subbuf_size;
@@ -608,9 +613,10 @@ struct rchan *relay_open(const char *base_filename,
 
 	mutex_lock(&relay_channels_mutex);
 	for_each_online_cpu(i) {
-		chan->buf[i] = relay_open_buf(chan, i);
-		if (!chan->buf[i])
+		buf = relay_open_buf(chan, i);
+		if (!buf)
 			goto free_bufs;
+		*per_cpu_ptr(chan->buf, i) = buf;
 	}
 	list_add(&chan->list, &relay_channels);
 	mutex_unlock(&relay_channels_mutex);
@@ -619,8 +625,8 @@ struct rchan *relay_open(const char *base_filename,
 
 free_bufs:
 	for_each_possible_cpu(i) {
-		if (chan->buf[i])
-			relay_close_buf(chan->buf[i]);
+		if ((buf = *per_cpu_ptr(chan->buf, i)))
+			relay_close_buf(buf);
 	}
 
 	kref_put(&chan->kref, relay_destroy_channel);
@@ -666,6 +672,7 @@ int relay_late_setup_files(struct rchan *chan,
 	unsigned int i, curr_cpu;
 	unsigned long flags;
 	struct dentry *dentry;
+	struct rchan_buf *buf;
 	struct rchan_percpu_buf_dispatcher disp;
 
 	if (!chan || !base_filename)
@@ -684,10 +691,11 @@ int relay_late_setup_files(struct rchan *chan,
 
 	if (chan->is_global) {
 		err = -EINVAL;
-		if (!WARN_ON_ONCE(!chan->buf[0])) {
-			dentry = relay_create_buf_file(chan, chan->buf[0], 0);
+		buf = *per_cpu_ptr(chan->buf, 0);
+		if (!WARN_ON_ONCE(!buf)) {
+			dentry = relay_create_buf_file(chan, buf, 0);
 			if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
-				relay_set_buf_dentry(chan->buf[0], dentry);
+				relay_set_buf_dentry(buf, dentry);
 				err = 0;
 			}
 		}
@@ -702,13 +710,14 @@ int relay_late_setup_files(struct rchan *chan,
 	 * on all currently online CPUs.
 	 */
 	for_each_online_cpu(i) {
-		if (unlikely(!chan->buf[i])) {
+		buf = *per_cpu_ptr(chan->buf, i);
+		if (unlikely(!buf)) {
 			WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
 			err = -EINVAL;
 			break;
 		}
 
-		dentry = relay_create_buf_file(chan, chan->buf[i], i);
+		dentry = relay_create_buf_file(chan, buf, i);
 		if (unlikely(!dentry)) {
 			err = -EINVAL;
 			break;
@@ -716,10 +725,10 @@ int relay_late_setup_files(struct rchan *chan,
 
 		if (curr_cpu == i) {
 			local_irq_save(flags);
-			relay_set_buf_dentry(chan->buf[i], dentry);
+			relay_set_buf_dentry(buf, dentry);
 			local_irq_restore(flags);
 		} else {
-			disp.buf = chan->buf[i];
+			disp.buf = buf;
 			disp.dentry = dentry;
 			smp_mb();
 			/* relay_channels_mutex must be held, so wait. */
@@ -822,11 +831,10 @@ void relay_subbufs_consumed(struct rchan *chan,
 	if (!chan)
 		return;
 
-	if (cpu >= NR_CPUS || !chan->buf[cpu] ||
-					subbufs_consumed > chan->n_subbufs)
+	buf = *per_cpu_ptr(chan->buf, cpu);
+	if (cpu >= NR_CPUS || !buf || subbufs_consumed > chan->n_subbufs)
 		return;
 
-	buf = chan->buf[cpu];
 	if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
 		buf->subbufs_consumed = buf->subbufs_produced;
 	else
@@ -842,18 +850,19 @@ EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
  */
 void relay_close(struct rchan *chan)
 {
+	struct rchan_buf *buf;
 	unsigned int i;
 
 	if (!chan)
 		return;
 
 	mutex_lock(&relay_channels_mutex);
-	if (chan->is_global && chan->buf[0])
-		relay_close_buf(chan->buf[0]);
+	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0)))
+		relay_close_buf(buf);
 	else
 		for_each_possible_cpu(i)
-			if (chan->buf[i])
-				relay_close_buf(chan->buf[i]);
+			if ((buf = *per_cpu_ptr(chan->buf, i)))
+				relay_close_buf(buf);
 
 	if (chan->last_toobig)
 		printk(KERN_WARNING "relay: one or more items not logged "
@@ -874,20 +883,21 @@ EXPORT_SYMBOL_GPL(relay_close);
  */
 void relay_flush(struct rchan *chan)
 {
+	struct rchan_buf *buf;
 	unsigned int i;
 
 	if (!chan)
 		return;
 
-	if (chan->is_global && chan->buf[0]) {
-		relay_switch_subbuf(chan->buf[0], 0);
+	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
+		relay_switch_subbuf(buf, 0);
 		return;
 	}
 
 	mutex_lock(&relay_channels_mutex);
 	for_each_possible_cpu(i)
-		if (chan->buf[i])
-			relay_switch_subbuf(chan->buf[i], 0);
+		if ((buf = *per_cpu_ptr(chan->buf, i)))
+			relay_switch_subbuf(buf, 0);
 	mutex_unlock(&relay_channels_mutex);
 }
 EXPORT_SYMBOL_GPL(relay_flush);