This patch stores stacktrace in the buffers to allow finding buffer leaks.
We use the option DM_DEBUG_BLOCK_STACK_TRACING.
The option DM_DEBUG_BLOCK_STACK_TRACING is moved from persistent-data
directory to device mapper directory because it will be used not only for
persistent data. When the option is enabled, each buffer stores the
stacktrace of the last dm_bufio_get, dm_bufio_read or dm_bufio_new call
that increased the hold count to 1. If the buffer is not released when the
bufio client is destroyed, the stacktrace is printed.
When DM_DEBUG_BLOCK_STACK_TRACING, the buffer leaks are considered
warnings - i.e. the kernel continues afterwards. If not, buffer leaks are
considered BUGs and the kernel crashes. I believe that if we made buffer
leaks always warnings, users would ignore them and the code would never be
fixed.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Index: linux-4.4-rc2/drivers/md/Kconfig
===================================================================
--- linux-4.4-rc2.orig/drivers/md/Kconfig
+++ linux-4.4-rc2/drivers/md/Kconfig
@@ -240,6 +240,15 @@ config DM_BUFIO
as a cache, holding recently-read blocks in memory and performing
delayed writes.
+config DM_DEBUG_BLOCK_STACK_TRACING
+ bool "Keep stack trace of persistent data block lock holders"
+ depends on STACKTRACE_SUPPORT && DM_BUFIO
+ select STACKTRACE
+ ---help---
+ Enable this for messages that may help debug problems with the
+ block manager locking used by thin provisioning and caching.
+
+ If unsure, say N.
config DM_BIO_PRISON
tristate
depends on BLK_DEV_DM
Index: linux-4.4-rc2/drivers/md/persistent-data/Kconfig
===================================================================
--- linux-4.4-rc2.orig/drivers/md/persistent-data/Kconfig
+++ linux-4.4-rc2/drivers/md/persistent-data/Kconfig
@@ -7,12 +7,3 @@ config DM_PERSISTENT_DATA
Library providing immutable on-disk data structure support for
device-mapper targets such as the thin provisioning target.
-config DM_DEBUG_BLOCK_STACK_TRACING
- bool "Keep stack trace of persistent data block lock holders"
- depends on STACKTRACE_SUPPORT && DM_PERSISTENT_DATA
- select STACKTRACE
- ---help---
- Enable this for messages that may help debug problems with the
- block manager locking used by thin provisioning and caching.
-
- If unsure, say N.
Index: linux-4.4-rc2/drivers/md/dm-bufio.c
===================================================================
--- linux-4.4-rc2.orig/drivers/md/dm-bufio.c
+++ linux-4.4-rc2/drivers/md/dm-bufio.c
@@ -16,6 +16,7 @@
#include <linux/shrinker.h>
#include <linux/module.h>
#include <linux/rbtree.h>
+#include <linux/stacktrace.h>
#define DM_MSG_PREFIX "bufio"
@@ -149,6 +150,11 @@ struct dm_buffer {
struct list_head write_list;
struct bio bio;
struct bio_vec bio_vec[DM_BUFIO_INLINE_VECS];
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+#define MAX_STACK 10
+ struct stack_trace stack_trace;
+ unsigned long stack_entries[MAX_STACK];
+#endif
};
/*----------------------------------------------------------------*/
@@ -253,6 +259,17 @@ static LIST_HEAD(dm_bufio_all_clients);
*/
static DEFINE_MUTEX(dm_bufio_clients_lock);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+static void buffer_record_stack(struct dm_buffer *b)
+{
+ b->stack_trace.nr_entries = 0;
+ b->stack_trace.max_entries = MAX_STACK;
+ b->stack_trace.entries = b->stack_entries;
+ b->stack_trace.skip = 2;
+ save_stack_trace(&b->stack_trace);
+}
+#endif
+
/*----------------------------------------------------------------
* A red/black tree acts as an index for all the buffers.
*--------------------------------------------------------------*/
@@ -454,6 +471,10 @@ static struct dm_buffer *alloc_buffer(st
adjust_total_allocated(b->data_mode, (long)c->block_size);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+ memset(&b->stack_trace, 0, sizeof b->stack_trace);
+#endif
+
return b;
}
@@ -1063,6 +1084,10 @@ static void *new_read(struct dm_bufio_cl
dm_bufio_lock(c);
b = __bufio_new(c, block, nf, &need_submit, &write_list);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+ if (b && b->hold_count == 1)
+ buffer_record_stack(b);
+#endif
dm_bufio_unlock(c);
__flush_write_list(&write_list);
@@ -1462,6 +1487,7 @@ static void drop_buffers(struct dm_bufio
{
struct dm_buffer *b;
int i;
+ bool warned = false;
BUG_ON(dm_bufio_in_request());
@@ -1476,9 +1502,21 @@ static void drop_buffers(struct dm_bufio
__free_buffer_wake(b);
for (i = 0; i < LIST_SIZE; i++)
- list_for_each_entry(b, &c->lru[i], lru_list)
+ list_for_each_entry(b, &c->lru[i], lru_list) {
+ WARN_ON(!warned);
+ warned = true;
DMERR("leaked buffer %llx, hold count %u, list %d",
(unsigned long long)b->block, b->hold_count, i);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+ print_stack_trace(&b->stack_trace, 1);
+ b->hold_count = 0; /* avoid the BUG */
+#endif
+ }
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+ while ((b = __get_unclaimed_buffer(c)))
+ __free_buffer_wake(b);
+#endif
for (i = 0; i < LIST_SIZE; i++)
BUG_ON(!list_empty(&c->lru[i]));
--
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