[dpdk-dev] [PATCH v2 7/7] mem: add thread unsafe version for checking DMA mask

[Alejandro Lucero <alejandro.lucero@netronome.com>]

During memory initialization calling rte_mem_check_dma_mask
leads to a deadlock because memory_hotplug_lock is locked by a
writer, the current code in execution, and rte_memseg_walk
tries to lock as a reader.

This patch adds a thread_unsafe version which will call the final
function specifying the memory_hotplug_lock does not need to be
acquired. The patch also modified rte_mem_check_dma_mask as a
intermediate step which will call the final function as before,
implying memory_hotplug_lock will be acquired.

PMDs should always use the version acquiring the lock with the
thread_unsafe one being just for internal EAL memory code.

Fixes: 223b7f1d5ef6 ("mem: add function for checking memseg IOVA")

Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>
---
 lib/librte_eal/common/eal_common_memory.c  | 24 +++++++++++++--
 lib/librte_eal/common/include/rte_memory.h | 35 +++++++++++++++++++---
 lib/librte_eal/common/malloc_heap.c        |  2 +-
 lib/librte_eal/linuxapp/eal/eal_memory.c   |  4 +--
 lib/librte_eal/rte_eal_version.map         |  1 +
 5 files changed, 56 insertions(+), 10 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_memory.c b/lib/librte_eal/common/eal_common_memory.c
index cc4f1d80f..87fd9921f 100644
--- a/lib/librte_eal/common/eal_common_memory.c
+++ b/lib/librte_eal/common/eal_common_memory.c
@@ -446,11 +446,12 @@ check_iova(const struct rte_memseg_list *msl __rte_unused,
 #endif
 
 /* check memseg iovas are within the required range based on dma mask */
-int __rte_experimental
-rte_mem_check_dma_mask(uint8_t maskbits)
+static int __rte_experimental
+check_dma_mask(uint8_t maskbits, bool thread_unsafe)
 {
 	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
 	uint64_t mask;
+	int ret;
 
 	/* sanity check */
 	if (maskbits > MAX_DMA_MASK_BITS) {
@@ -462,7 +463,12 @@ rte_mem_check_dma_mask(uint8_t maskbits)
 	/* create dma mask */
 	mask = ~((1ULL << maskbits) - 1);
 
-	if (rte_memseg_walk(check_iova, &mask))
+	if (thread_unsafe)
+		ret = rte_memseg_walk_thread_unsafe(check_iova, &mask);
+	else
+		ret = rte_memseg_walk(check_iova, &mask);
+
+	if (ret)
 		/*
 		 * Dma mask precludes hugepage usage.
 		 * This device can not be used and we do not need to keep
@@ -480,6 +486,18 @@ rte_mem_check_dma_mask(uint8_t maskbits)
 	return 0;
 }
 
+int __rte_experimental
+rte_mem_check_dma_mask(uint8_t maskbits)
+{
+	return check_dma_mask(maskbits, false);
+}
+
+int __rte_experimental
+rte_mem_check_dma_mask_thread_unsafe(uint8_t maskbits)
+{
+	return check_dma_mask(maskbits, true);
+}
+
 /*
  * Set dma mask to use when memory initialization is done.
  *
diff --git a/lib/librte_eal/common/include/rte_memory.h b/lib/librte_eal/common/include/rte_memory.h
index abbfe2364..d970825df 100644
--- a/lib/librte_eal/common/include/rte_memory.h
+++ b/lib/librte_eal/common/include/rte_memory.h
@@ -463,16 +463,43 @@ unsigned rte_memory_get_nchannel(void);
  */
 unsigned rte_memory_get_nrank(void);
 
-/* check memsegs iovas are within a range based on dma mask */
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice
+ *
+ * Check if all currently allocated memory segments are compliant with
+ * supplied DMA address width.
+ *
+ *  @param maskbits
+ *    Address width to check against.
+ */
 int __rte_experimental rte_mem_check_dma_mask(uint8_t maskbits);
 
 /**
  * @warning
  * @b EXPERIMENTAL: this API may change without prior notice
  *
- *  Set dma mask to use once memory initialization is done.
- *  Previous function rte_mem_check_dma_mask can not be used
- *  safely until memory has been initialized.
+ * Check if all currently allocated memory segments are compliant with
+ * supplied DMA address width. This function will use
+ * rte_memseg_walk_thread_unsafe instead of rte_memseg_walk implying
+ * memory_hotplug_lock will not be acquired avoiding deadlock during
+ * memory initialization.
+ *
+ * This function is just for EAL core memory internal use. Drivers should
+ * use the previous rte_mem_check_dma_mask.
+ *
+ *  @param maskbits
+ *    Address width to check against.
+ */
+int __rte_experimental rte_mem_check_dma_mask_thread_unsafe(uint8_t maskbits);
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice
+ *
+ *  Set dma mask to use once memory initialization is done. Previous functions
+ *  rte_mem_check_dma_mask and rte_mem_check_dma_mask_thread_unsafe can not be
+ *  used safely until memory has been initialized.
  */
 void __rte_experimental rte_mem_set_dma_mask(uint8_t maskbits);
 
diff --git a/lib/librte_eal/common/malloc_heap.c b/lib/librte_eal/common/malloc_heap.c
index c2c112aa6..c6a6d4f6b 100644
--- a/lib/librte_eal/common/malloc_heap.c
+++ b/lib/librte_eal/common/malloc_heap.c
@@ -334,7 +334,7 @@ alloc_pages_on_heap(struct malloc_heap *heap, uint64_t pg_sz, size_t elt_size,
 	 * executed. For 2) implies the new memory can not be added.
 	 */
 	if (mcfg->dma_maskbits &&
-	    rte_mem_check_dma_mask(mcfg->dma_maskbits)) {
+	    rte_mem_check_dma_mask_thread_unsafe(mcfg->dma_maskbits)) {
 		/*
 		 * Currently this can only happen if IOMMU is enabled
 		 * and the address width supported by the IOMMU hw is
diff --git a/lib/librte_eal/linuxapp/eal/eal_memory.c b/lib/librte_eal/linuxapp/eal/eal_memory.c
index c7935879a..c1b5e0791 100644
--- a/lib/librte_eal/linuxapp/eal/eal_memory.c
+++ b/lib/librte_eal/linuxapp/eal/eal_memory.c
@@ -1394,7 +1394,7 @@ eal_legacy_hugepage_init(void)
 			addr = RTE_PTR_ADD(addr, (size_t)page_sz);
 		}
 		if (mcfg->dma_maskbits &&
-		    rte_mem_check_dma_mask(mcfg->dma_maskbits)) {
+		    rte_mem_check_dma_mask_thread_unsafe(mcfg->dma_maskbits)) {
 			RTE_LOG(ERR, EAL,
 				"%s(): couldnt allocate memory due to IOVA exceeding limits of current DMA mask.\n",
 				__func__);
@@ -1641,7 +1641,7 @@ eal_legacy_hugepage_init(void)
 	}
 
 	if (mcfg->dma_maskbits &&
-	    rte_mem_check_dma_mask(mcfg->dma_maskbits)) {
+	    rte_mem_check_dma_mask_thread_unsafe(mcfg->dma_maskbits)) {
 		RTE_LOG(ERR, EAL,
 			"%s(): couldn't allocate memory due to IOVA exceeding limits of current DMA mask.\n",
 			__func__);
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index 51ee948ba..61bc5ca05 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -331,6 +331,7 @@ EXPERIMENTAL {
 	rte_mem_alloc_validator_register;
 	rte_mem_alloc_validator_unregister;
 	rte_mem_check_dma_mask;
+	rte_mem_check_dma_mask_thread_unsafe;
 	rte_mem_event_callback_register;
 	rte_mem_event_callback_unregister;
 	rte_mem_iova2virt;
-- 
2.17.1