[dpdk-dev] [PATCH 19.02 v2] malloc: fix deadlock when using malloc stats

[Anatoly Burakov <anatoly.burakov@intel.com>]

Currently, malloc statistics and external heap creation code
use memory hotplug lock as a way to synchronize accesses to
heaps (as in, locking the hotplug lock to prevent list of heaps
from changing under our feet). At the same time, malloc
statistics code will also lock the heap because it needs to
access heap data and does not want any other thread to allocate
anything from that heap.

In such scheme, it is possible to enter a deadlock with the
following sequence of events:

thread 1		thread 2
rte_malloc()
			rte_malloc_dump_stats()
take heap lock
			take hotplug lock
failed to allocate,
attempt to take
hotplug lock
			attempt to take heap lock

Neither thread will be able to continue, as both of them are
waiting for the other one to drop the lock. Adding an
additional lock will require an ABI change, so instead of
that, make malloc statistics calls thread-unsafe with
respect to creating/destroying heaps.

Fixes: 72cf92b31855 ("malloc: index heaps using heap ID rather than NUMA node")
Cc: stable@dpdk.org

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---

Notes:
    This is the best we can do for 19.02 without breaking ABI.

 doc/guides/rel_notes/release_19_02.rst     |  4 ++++
 lib/librte_eal/common/include/rte_malloc.h |  9 +++++++++
 lib/librte_eal/common/rte_malloc.c         | 19 +++----------------
 3 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/doc/guides/rel_notes/release_19_02.rst b/doc/guides/rel_notes/release_19_02.rst
index 47768288a..0b248d55d 100644
--- a/doc/guides/rel_notes/release_19_02.rst
+++ b/doc/guides/rel_notes/release_19_02.rst
@@ -126,6 +126,10 @@ API Changes
   - In cases where memfd support would have been required to provide segment
     fd's (such as in-memory or no-huge mode)
 
+* eal: Functions ``rte_malloc_dump_stats()``, ``rte_malloc_dump_heaps()`` and
+  ``rte_malloc_get_socket_stats()`` are no longer safe to call concurrently with
+  ``rte_malloc_heap_create()`` or ``rte_malloc_heap_destroy()`` function calls.
+
 * pdump: The ``rte_pdump_set_socket_dir()``, the parameter ``path`` of
   ``rte_pdump_init()`` and enum ``rte_pdump_socktype`` were deprecated
   since 18.05 and are removed in this release.
diff --git a/lib/librte_eal/common/include/rte_malloc.h b/lib/librte_eal/common/include/rte_malloc.h
index a5290b074..54a12467a 100644
--- a/lib/librte_eal/common/include/rte_malloc.h
+++ b/lib/librte_eal/common/include/rte_malloc.h
@@ -251,6 +251,9 @@ rte_malloc_validate(const void *ptr, size_t *size);
 /**
  * Get heap statistics for the specified heap.
  *
+ * @note This function is not thread-safe with respect to
+ *    ``rte_malloc_heap_create()``/``rte_malloc_heap_destroy()`` functions.
+ *
  * @param socket
  *   An unsigned integer specifying the socket to get heap statistics for
  * @param socket_stats
@@ -461,6 +464,9 @@ rte_malloc_heap_socket_is_external(int socket_id);
  * Dump for the specified type to a file. If the type argument is
  * NULL, all memory types will be dumped.
  *
+ * @note This function is not thread-safe with respect to
+ *    ``rte_malloc_heap_create()``/``rte_malloc_heap_destroy()`` functions.
+ *
  * @param f
  *   A pointer to a file for output
  * @param type
@@ -473,6 +479,9 @@ rte_malloc_dump_stats(FILE *f, const char *type);
 /**
  * Dump contents of all malloc heaps to a file.
  *
+ * @note This function is not thread-safe with respect to
+ *    ``rte_malloc_heap_create()``/``rte_malloc_heap_destroy()`` functions.
+ *
  * @param f
  *   A pointer to a file for output
  */
diff --git a/lib/librte_eal/common/rte_malloc.c b/lib/librte_eal/common/rte_malloc.c
index 09051c236..b39de3c99 100644
--- a/lib/librte_eal/common/rte_malloc.c
+++ b/lib/librte_eal/common/rte_malloc.c
@@ -156,20 +156,14 @@ rte_malloc_get_socket_stats(int socket,
 		struct rte_malloc_socket_stats *socket_stats)
 {
 	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
-	int heap_idx, ret = -1;
-
-	rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
+	int heap_idx;
 
 	heap_idx = malloc_socket_to_heap_id(socket);
 	if (heap_idx < 0)
-		goto unlock;
+		return -1;
 
-	ret = malloc_heap_get_stats(&mcfg->malloc_heaps[heap_idx],
+	return malloc_heap_get_stats(&mcfg->malloc_heaps[heap_idx],
 			socket_stats);
-unlock:
-	rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
-
-	return ret;
 }
 
 /*
@@ -181,14 +175,10 @@ rte_malloc_dump_heaps(FILE *f)
 	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
 	unsigned int idx;
 
-	rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
-
 	for (idx = 0; idx < RTE_MAX_HEAPS; idx++) {
 		fprintf(f, "Heap id: %u\n", idx);
 		malloc_heap_dump(&mcfg->malloc_heaps[idx], f);
 	}
-
-	rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
 }
 
 int
@@ -262,8 +252,6 @@ rte_malloc_dump_stats(FILE *f, __rte_unused const char *type)
 	unsigned int heap_id;
 	struct rte_malloc_socket_stats sock_stats;
 
-	rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
-
 	/* Iterate through all initialised heaps */
 	for (heap_id = 0; heap_id < RTE_MAX_HEAPS; heap_id++) {
 		struct malloc_heap *heap = &mcfg->malloc_heaps[heap_id];
@@ -280,7 +268,6 @@ rte_malloc_dump_stats(FILE *f, __rte_unused const char *type)
 		fprintf(f, "\tAlloc_count:%u,\n",sock_stats.alloc_count);
 		fprintf(f, "\tFree_count:%u,\n", sock_stats.free_count);
 	}
-	rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
 	return;
 }
 
-- 
2.17.1