libibverbs: Undo changes in memory range tree when madvise() fails

ibv_madvise_range() doesn't cleanup if madvise() fails. This patch comes to roll back the changes, made in memory tree, which preceded the madvise() failure:

When madvise() fails on a memory range portion out of the whole range which user requested to modify and ibv_madvise_range() successfully modified a few tree nodes up to the problematical portion sub-ranges (this can happen if there is an overlap between user's range and range's which where previously added to the memory tree) then it is not enough to undo the split and merge operation performed on the current node, which caused the failure, but the functions needed to undo all the changes made on all the previous ranges from start pointer to current location.
The patch revertes all the changes by re-running it self from start pointer to current location with toggled inc value.

Signed-off-by Alex Vainman <alexv-smomgflXvOZWk0Htik3J/[email protected]>

---
 src/memory.c |   21 ++++++++++++++++++---
 1 files changed, 18 insertions(+), 3 deletions(-)

src/memory.c +16 -3

index 03f49c8..14f5bc5 100644
@@ -527,18 +527,19 @@ static int ibv_madvise_range(void *base, size_t size, int advice)
 	uintptr_t start, end;
 	struct ibv_mem_node *node, *tmp;
 	int inc;
+	int rolling_back = 0;
 	int ret = 0;
 
 	if (!size)
 		return 0;
 
-	inc = advice == MADV_DONTFORK ? 1 : -1;
-
 	start = (uintptr_t) base & ~(page_size - 1);
 	end   = ((uintptr_t) (base + size + page_size - 1) &
 		 ~(page_size - 1)) - 1;
 
 	pthread_mutex_lock(&mm_mutex);
+again:
+	inc = advice == MADV_DONTFORK ? 1 : -1;
 
 	node = get_start_node(start, end, inc);
 	if (!node) {

@@ -576,7 +577,19 @@ static int ibv_madvise_range(void *base, size_t size, int advice)
 					      advice);
 			if (ret) {
 				node = undo_node(node, start, inc);
-				goto out;
+
+				if (rolling_back || !node)
+					goto out;
+
+				/* madvise failed, roll back previous changes */
+				rolling_back = 1;
+				advice = advice == MADV_DONTFORK ? MADV_DOFORK :
+								   MADV_DONTFORK;
+				tmp = __mm_prev(node);
+				if (!tmp || start > tmp->end)
+					goto out;
+				end = tmp->end;
+				goto again;
 			}
 		}