X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=lib%2Fringbuffer%2Fring_buffer_frontend.c;h=5d4be3b3dcf4ddc60920377c3d1f160ceb629261;hb=fbe84fd748b6fde1f773da8e44d61235f8d4c232;hp=c4b797ce8af76faf9ba5209d054b89fb42326656;hpb=e6b06d7d6346a5e3cfcdd214d171af067bca0f34;p=lttng-modules.git

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index c4b797ce..5d4be3b3 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -55,13 +55,15 @@
 #include <linux/module.h>
 #include <linux/percpu.h>
 
-#include "../../wrapper/ringbuffer/config.h"
-#include "../../wrapper/ringbuffer/backend.h"
-#include "../../wrapper/ringbuffer/frontend.h"
-#include "../../wrapper/ringbuffer/iterator.h"
-#include "../../wrapper/ringbuffer/nohz.h"
-#include "../../wrapper/atomic.h"
-#include "../../wrapper/percpu-defs.h"
+#include <wrapper/ringbuffer/config.h>
+#include <wrapper/ringbuffer/backend.h>
+#include <wrapper/ringbuffer/frontend.h>
+#include <wrapper/ringbuffer/iterator.h>
+#include <wrapper/ringbuffer/nohz.h>
+#include <wrapper/atomic.h>
+#include <wrapper/kref.h>
+#include <wrapper/percpu-defs.h>
+#include <wrapper/timer.h>
 
 /*
  * Internal structure representing offsets to use at a sub-buffer switch.
@@ -91,6 +93,50 @@ EXPORT_PER_CPU_SYMBOL(lib_ring_buffer_nesting);
 static
 void lib_ring_buffer_print_errors(struct channel *chan,
 				  struct lib_ring_buffer *buf, int cpu);
+static
+void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
+		enum switch_mode mode);
+
+static
+int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config *config,
+				 struct lib_ring_buffer *buf,
+			         struct channel *chan)
+{
+	unsigned long consumed_old, consumed_idx, commit_count, write_offset;
+
+	consumed_old = atomic_long_read(&buf->consumed);
+	consumed_idx = subbuf_index(consumed_old, chan);
+	commit_count = v_read(config, &buf->commit_cold[consumed_idx].cc_sb);
+	/*
+	 * No memory barrier here, since we are only interested
+	 * in a statistically correct polling result. The next poll will
+	 * get the data is we are racing. The mb() that ensures correct
+	 * memory order is in get_subbuf.
+	 */
+	write_offset = v_read(config, &buf->offset);
+
+	/*
+	 * Check that the subbuffer we are trying to consume has been
+	 * already fully committed.
+	 */
+
+	if (((commit_count - chan->backend.subbuf_size)
+	     & chan->commit_count_mask)
+	    - (buf_trunc(consumed_old, chan)
+	       >> chan->backend.num_subbuf_order)
+	    != 0)
+		return 0;
+
+	/*
+	 * Check that we are not about to read the same subbuffer in
+	 * which the writer head is.
+	 */
+	if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed_old, chan)
+	    == 0)
+		return 0;
+
+	return 1;
+}
 
 /*
  * Must be called under cpu hotplug protection.
@@ -201,7 +247,8 @@ int lib_ring_buffer_create(struct lib_ring_buffer *buf,
 		kzalloc_node(ALIGN(sizeof(*buf->commit_hot)
 				   * chan->backend.num_subbuf,
 				   1 << INTERNODE_CACHE_SHIFT),
-			GFP_KERNEL, cpu_to_node(max(cpu, 0)));
+			GFP_KERNEL | __GFP_NOWARN,
+			cpu_to_node(max(cpu, 0)));
 	if (!buf->commit_hot) {
 		ret = -ENOMEM;
 		goto free_chanbuf;
@@ -211,7 +258,8 @@ int lib_ring_buffer_create(struct lib_ring_buffer *buf,
 		kzalloc_node(ALIGN(sizeof(*buf->commit_cold)
 				   * chan->backend.num_subbuf,
 				   1 << INTERNODE_CACHE_SHIFT),
-			GFP_KERNEL, cpu_to_node(max(cpu, 0)));
+			GFP_KERNEL | __GFP_NOWARN,
+			cpu_to_node(max(cpu, 0)));
 	if (!buf->commit_cold) {
 		ret = -ENOMEM;
 		goto free_commit;
@@ -277,7 +325,7 @@ static void switch_buffer_timer(unsigned long data)
 		lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
 
 	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
-		mod_timer_pinned(&buf->switch_timer,
+		lttng_mod_timer_pinned(&buf->switch_timer,
 				 jiffies + chan->switch_timer_interval);
 	else
 		mod_timer(&buf->switch_timer,
@@ -294,7 +342,12 @@ static void lib_ring_buffer_start_switch_timer(struct lib_ring_buffer *buf)
 
 	if (!chan->switch_timer_interval || buf->switch_timer_enabled)
 		return;
-	init_timer(&buf->switch_timer);
+
+	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+		lttng_init_timer_pinned(&buf->switch_timer);
+	else
+		init_timer(&buf->switch_timer);
+
 	buf->switch_timer.function = switch_buffer_timer;
 	buf->switch_timer.expires = jiffies + chan->switch_timer_interval;
 	buf->switch_timer.data = (unsigned long)buf;
@@ -337,7 +390,7 @@ static void read_buffer_timer(unsigned long data)
 	}
 
 	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
-		mod_timer_pinned(&buf->read_timer,
+		lttng_mod_timer_pinned(&buf->read_timer,
 				 jiffies + chan->read_timer_interval);
 	else
 		mod_timer(&buf->read_timer,
@@ -357,7 +410,11 @@ static void lib_ring_buffer_start_read_timer(struct lib_ring_buffer *buf)
 	    || buf->read_timer_enabled)
 		return;
 
-	init_timer(&buf->read_timer);
+	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+		lttng_init_timer_pinned(&buf->read_timer);
+	else
+		init_timer(&buf->read_timer);
+
 	buf->read_timer.function = read_buffer_timer;
 	buf->read_timer.expires = jiffies + chan->read_timer_interval;
 	buf->read_timer.data = (unsigned long)buf;
@@ -585,6 +642,63 @@ static void channel_unregister_notifiers(struct channel *chan)
 	channel_backend_unregister_notifiers(&chan->backend);
 }
 
+static void lib_ring_buffer_set_quiescent(struct lib_ring_buffer *buf)
+{
+	if (!buf->quiescent) {
+		buf->quiescent = true;
+		_lib_ring_buffer_switch_remote(buf, SWITCH_FLUSH);
+	}
+}
+
+static void lib_ring_buffer_clear_quiescent(struct lib_ring_buffer *buf)
+{
+	buf->quiescent = false;
+}
+
+void lib_ring_buffer_set_quiescent_channel(struct channel *chan)
+{
+	int cpu;
+	const struct lib_ring_buffer_config *config = &chan->backend.config;
+
+	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+		get_online_cpus();
+		for_each_channel_cpu(cpu, chan) {
+			struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+							      cpu);
+
+			lib_ring_buffer_set_quiescent(buf);
+		}
+		put_online_cpus();
+	} else {
+		struct lib_ring_buffer *buf = chan->backend.buf;
+
+		lib_ring_buffer_set_quiescent(buf);
+	}
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_set_quiescent_channel);
+
+void lib_ring_buffer_clear_quiescent_channel(struct channel *chan)
+{
+	int cpu;
+	const struct lib_ring_buffer_config *config = &chan->backend.config;
+
+	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+		get_online_cpus();
+		for_each_channel_cpu(cpu, chan) {
+			struct lib_ring_buffer *buf = per_cpu_ptr(chan->backend.buf,
+							      cpu);
+
+			lib_ring_buffer_clear_quiescent(buf);
+		}
+		put_online_cpus();
+	} else {
+		struct lib_ring_buffer *buf = chan->backend.buf;
+
+		lib_ring_buffer_clear_quiescent(buf);
+	}
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_clear_quiescent_channel);
+
 static void channel_free(struct channel *chan)
 {
 	if (chan->backend.release_priv_ops) {
@@ -745,7 +859,7 @@ void *channel_destroy(struct channel *chan)
 							   chan->backend.priv,
 							   cpu);
 			if (buf->backend.allocated)
-				lib_ring_buffer_switch_slow(buf, SWITCH_FLUSH);
+				lib_ring_buffer_set_quiescent(buf);
 			/*
 			 * Perform flush before writing to finalized.
 			 */
@@ -759,7 +873,7 @@ void *channel_destroy(struct channel *chan)
 		if (config->cb.buffer_finalize)
 			config->cb.buffer_finalize(buf, chan->backend.priv, -1);
 		if (buf->backend.allocated)
-			lib_ring_buffer_switch_slow(buf, SWITCH_FLUSH);
+			lib_ring_buffer_set_quiescent(buf);
 		/*
 		 * Perform flush before writing to finalized.
 		 */
@@ -793,7 +907,10 @@ int lib_ring_buffer_open_read(struct lib_ring_buffer *buf)
 
 	if (!atomic_long_add_unless(&buf->active_readers, 1, 1))
 		return -EBUSY;
-	kref_get(&chan->ref);
+	if (!lttng_kref_get(&chan->ref)) {
+		atomic_long_dec(&buf->active_readers);
+		return -EOVERFLOW;
+	}
 	lttng_smp_mb__after_atomic();
 	return 0;
 }
@@ -1229,7 +1346,8 @@ void lib_ring_buffer_print_errors(struct channel *chan,
 /*
  * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
  *
- * Only executed when the buffer is finalized, in SWITCH_FLUSH.
+ * Only executed by SWITCH_FLUSH, which can be issued while tracing is active
+ * or at buffer finalization (destroy).
  */
 static
 void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
@@ -1240,6 +1358,7 @@ void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
 	const struct lib_ring_buffer_config *config = &chan->backend.config;
 	unsigned long oldidx = subbuf_index(offsets->old, chan);
 	unsigned long commit_count;
+	struct commit_counters_hot *cc_hot;
 
 	config->cb.buffer_begin(buf, tsc, oldidx);
 
@@ -1256,15 +1375,15 @@ void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
 		barrier();
 	} else
 		smp_wmb();
-	v_add(config, config->cb.subbuffer_header_size(),
-	      &buf->commit_hot[oldidx].cc);
-	commit_count = v_read(config, &buf->commit_hot[oldidx].cc);
+	cc_hot = &buf->commit_hot[oldidx];
+	v_add(config, config->cb.subbuffer_header_size(), &cc_hot->cc);
+	commit_count = v_read(config, &cc_hot->cc);
 	/* Check if the written buffer has to be delivered */
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old,
 				      commit_count, oldidx, tsc);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
 			offsets->old + config->cb.subbuffer_header_size(),
-			commit_count);
+			commit_count, cc_hot);
 }
 
 /*
@@ -1284,6 +1403,7 @@ void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf,
 	const struct lib_ring_buffer_config *config = &chan->backend.config;
 	unsigned long oldidx = subbuf_index(offsets->old - 1, chan);
 	unsigned long commit_count, padding_size, data_size;
+	struct commit_counters_hot *cc_hot;
 
 	data_size = subbuf_offset(offsets->old - 1, chan) + 1;
 	padding_size = chan->backend.subbuf_size - data_size;
@@ -1302,12 +1422,14 @@ void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf,
 		barrier();
 	} else
 		smp_wmb();
-	v_add(config, padding_size, &buf->commit_hot[oldidx].cc);
-	commit_count = v_read(config, &buf->commit_hot[oldidx].cc);
+	cc_hot = &buf->commit_hot[oldidx];
+	v_add(config, padding_size, &cc_hot->cc);
+	commit_count = v_read(config, &cc_hot->cc);
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1,
 				      commit_count, oldidx, tsc);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
-			offsets->old + padding_size, commit_count);
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
+			offsets->old + padding_size, commit_count,
+			cc_hot);
 }
 
 /*
@@ -1326,6 +1448,7 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
 	const struct lib_ring_buffer_config *config = &chan->backend.config;
 	unsigned long beginidx = subbuf_index(offsets->begin, chan);
 	unsigned long commit_count;
+	struct commit_counters_hot *cc_hot;
 
 	config->cb.buffer_begin(buf, tsc, beginidx);
 
@@ -1342,15 +1465,15 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
 		barrier();
 	} else
 		smp_wmb();
-	v_add(config, config->cb.subbuffer_header_size(),
-	      &buf->commit_hot[beginidx].cc);
-	commit_count = v_read(config, &buf->commit_hot[beginidx].cc);
+	cc_hot = &buf->commit_hot[beginidx];
+	v_add(config, config->cb.subbuffer_header_size(), &cc_hot->cc);
+	commit_count = v_read(config, &cc_hot->cc);
 	/* Check if the written buffer has to be delivered */
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin,
 				      commit_count, beginidx, tsc);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx,
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
 			offsets->begin + config->cb.subbuffer_header_size(),
-			commit_count);
+			commit_count, cc_hot);
 }
 
 /*
@@ -1420,12 +1543,14 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode,
 		unsigned long sb_index, commit_count;
 
 		/*
-		 * We are performing a SWITCH_FLUSH. At this stage, there are no
-		 * concurrent writes into the buffer.
+		 * We are performing a SWITCH_FLUSH. There may be concurrent
+		 * writes into the buffer if e.g. invoked while performing a
+		 * snapshot on an active trace.
 		 *
-		 * The client does not save any header information.  Don't
-		 * switch empty subbuffer on finalize, because it is invalid to
-		 * deliver a completely empty subbuffer.
+		 * If the client does not save any header information (sub-buffer
+		 * header size == 0), don't switch empty subbuffer on finalize,
+		 * because it is invalid to deliver a completely empty
+		 * subbuffer.
 		 */
 		if (!config->cb.subbuffer_header_size())
 			return -1;
@@ -1539,24 +1664,32 @@ void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf, enum switch_mode m
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow);
 
+struct switch_param {
+	struct lib_ring_buffer *buf;
+	enum switch_mode mode;
+};
+
 static void remote_switch(void *info)
 {
-	struct lib_ring_buffer *buf = info;
+	struct switch_param *param = info;
+	struct lib_ring_buffer *buf = param->buf;
 
-	lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+	lib_ring_buffer_switch_slow(buf, param->mode);
 }
 
-void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
+static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
+		enum switch_mode mode)
 {
 	struct channel *chan = buf->backend.chan;
 	const struct lib_ring_buffer_config *config = &chan->backend.config;
 	int ret;
+	struct switch_param param;
 
 	/*
 	 * With global synchronization we don't need to use the IPI scheme.
 	 */
 	if (config->sync == RING_BUFFER_SYNC_GLOBAL) {
-		lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+		lib_ring_buffer_switch_slow(buf, mode);
 		return;
 	}
 
@@ -1571,16 +1704,30 @@ void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
 	 * switch.
 	 */
 	get_online_cpus();
+	param.buf = buf;
+	param.mode = mode;
 	ret = smp_call_function_single(buf->backend.cpu,
-				 remote_switch, buf, 1);
+				 remote_switch, &param, 1);
 	if (ret) {
 		/* Remote CPU is offline, do it ourself. */
-		lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+		lib_ring_buffer_switch_slow(buf, mode);
 	}
 	put_online_cpus();
 }
+
+void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
+{
+	_lib_ring_buffer_switch_remote(buf, SWITCH_ACTIVE);
+}
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote);
 
+/* Switch sub-buffer even if current sub-buffer is empty. */
+void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf)
+{
+	_lib_ring_buffer_switch_remote(buf, SWITCH_FLUSH);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote_empty);
+
 /*
  * Returns :
  * 0 if ok
@@ -1739,6 +1886,25 @@ retry:
 	return 0;
 }
 
+static struct lib_ring_buffer *get_current_buf(struct channel *chan, int cpu)
+{
+	const struct lib_ring_buffer_config *config = &chan->backend.config;
+
+	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
+		return per_cpu_ptr(chan->backend.buf, cpu);
+	else
+		return chan->backend.buf;
+}
+
+void lib_ring_buffer_lost_event_too_big(struct channel *chan)
+{
+	const struct lib_ring_buffer_config *config = &chan->backend.config;
+	struct lib_ring_buffer *buf = get_current_buf(chan, smp_processor_id());
+
+	v_inc(config, &buf->records_lost_big);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_lost_event_too_big);
+
 /**
  * lib_ring_buffer_reserve_slow - Atomic slot reservation in a buffer.
  * @ctx: ring buffer context.
@@ -1755,12 +1921,7 @@ int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx)
 	struct switch_offsets offsets;
 	int ret;
 
-	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
-		buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
-	else
-		buf = chan->backend.buf;
-	ctx->buf = buf;
-
+	ctx->buf = buf = get_current_buf(chan, ctx->cpu);
 	offsets.size = 0;
 
 	do {
@@ -1816,6 +1977,147 @@ int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx)
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_reserve_slow);
 
+static
+void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config *config,
+					  struct lib_ring_buffer *buf,
+				          unsigned long commit_count,
+				          unsigned long idx)
+{
+	if (config->oops == RING_BUFFER_OOPS_CONSISTENCY)
+		v_set(config, &buf->commit_hot[idx].seq, commit_count);
+}
+
+/*
+ * The ring buffer can count events recorded and overwritten per buffer,
+ * but it is disabled by default due to its performance overhead.
+ */
+#ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
+static
+void deliver_count_events(const struct lib_ring_buffer_config *config,
+		struct lib_ring_buffer *buf,
+		unsigned long idx)
+{
+	v_add(config, subbuffer_get_records_count(config,
+			&buf->backend, idx),
+		&buf->records_count);
+	v_add(config, subbuffer_count_records_overrun(config,
+			&buf->backend, idx),
+		&buf->records_overrun);
+}
+#else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
+static
+void deliver_count_events(const struct lib_ring_buffer_config *config,
+		struct lib_ring_buffer *buf,
+		unsigned long idx)
+{
+}
+#endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
+
+
+void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config *config,
+				   struct lib_ring_buffer *buf,
+			           struct channel *chan,
+			           unsigned long offset,
+				   unsigned long commit_count,
+			           unsigned long idx,
+				   u64 tsc)
+{
+	unsigned long old_commit_count = commit_count
+					 - chan->backend.subbuf_size;
+
+	/*
+	 * If we succeeded at updating cc_sb below, we are the subbuffer
+	 * writer delivering the subbuffer. Deals with concurrent
+	 * updates of the "cc" value without adding a add_return atomic
+	 * operation to the fast path.
+	 *
+	 * We are doing the delivery in two steps:
+	 * - First, we cmpxchg() cc_sb to the new value
+	 *   old_commit_count + 1. This ensures that we are the only
+	 *   subbuffer user successfully filling the subbuffer, but we
+	 *   do _not_ set the cc_sb value to "commit_count" yet.
+	 *   Therefore, other writers that would wrap around the ring
+	 *   buffer and try to start writing to our subbuffer would
+	 *   have to drop records, because it would appear as
+	 *   non-filled.
+	 *   We therefore have exclusive access to the subbuffer control
+	 *   structures.  This mutual exclusion with other writers is
+	 *   crucially important to perform record overruns count in
+	 *   flight recorder mode locklessly.
+	 * - When we are ready to release the subbuffer (either for
+	 *   reading or for overrun by other writers), we simply set the
+	 *   cc_sb value to "commit_count" and perform delivery.
+	 *
+	 * The subbuffer size is least 2 bytes (minimum size: 1 page).
+	 * This guarantees that old_commit_count + 1 != commit_count.
+	 */
+
+	/*
+	 * Order prior updates to reserve count prior to the
+	 * commit_cold cc_sb update.
+	 */
+	smp_wmb();
+	if (likely(v_cmpxchg(config, &buf->commit_cold[idx].cc_sb,
+				 old_commit_count, old_commit_count + 1)
+		   == old_commit_count)) {
+		/*
+		 * Start of exclusive subbuffer access. We are
+		 * guaranteed to be the last writer in this subbuffer
+		 * and any other writer trying to access this subbuffer
+		 * in this state is required to drop records.
+		 */
+		deliver_count_events(config, buf, idx);
+		config->cb.buffer_end(buf, tsc, idx,
+				      lib_ring_buffer_get_data_size(config,
+								buf,
+								idx));
+
+		/*
+		 * Increment the packet counter while we have exclusive
+		 * access.
+		 */
+		subbuffer_inc_packet_count(config, &buf->backend, idx);
+
+		/*
+		 * Set noref flag and offset for this subbuffer id.
+		 * Contains a memory barrier that ensures counter stores
+		 * are ordered before set noref and offset.
+		 */
+		lib_ring_buffer_set_noref_offset(config, &buf->backend, idx,
+						 buf_trunc_val(offset, chan));
+
+		/*
+		 * Order set_noref and record counter updates before the
+		 * end of subbuffer exclusive access. Orders with
+		 * respect to writers coming into the subbuffer after
+		 * wrap around, and also order wrt concurrent readers.
+		 */
+		smp_mb();
+		/* End of exclusive subbuffer access */
+		v_set(config, &buf->commit_cold[idx].cc_sb,
+		      commit_count);
+		/*
+		 * Order later updates to reserve count after
+		 * the commit_cold cc_sb update.
+		 */
+		smp_wmb();
+		lib_ring_buffer_vmcore_check_deliver(config, buf,
+						 commit_count, idx);
+
+		/*
+		 * RING_BUFFER_WAKEUP_BY_WRITER wakeup is not lock-free.
+		 */
+		if (config->wakeup == RING_BUFFER_WAKEUP_BY_WRITER
+		    && atomic_long_read(&buf->active_readers)
+		    && lib_ring_buffer_poll_deliver(config, buf, chan)) {
+			wake_up_interruptible(&buf->read_wait);
+			wake_up_interruptible(&chan->read_wait);
+		}
+
+	}
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_check_deliver_slow);
+
 int __init init_lib_ring_buffer_frontend(void)
 {
 	int cpu;