[PATCH] maple_tree: Remove warning from mas_nomem()

[Liam R. Howlett (Oracle)]

It is possible to trigger the warning in mas_nomem in certain call paths
using valid gfp flags.  Drop the warning and handle the failures
differently.

Instead, have mtree_erase() and mas_erase() use __GFP_NOFAIL.

During the discussion, mas_store() was also flagged as a potential path
that may fail due to implied gfp flags.  Changing those flags to retry
with __GFP_NOFAIL is a viable solution there.  At the same time, adding
a might_sleep() check to catch incorrect uses is prudent.

Signed-off-by: Liam R. Howlett (Oracle) <liam@xxxxxxxxxxxxx>
---
 lib/maple_tree.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 0954d431bf981..4fb7a209dcb2d 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5577,6 +5577,9 @@ void *mas_store(struct ma_state *mas, void *entry)
 	MA_WR_STATE(wr_mas, mas, entry);
 
 	mas_may_init_lock_check(mas);
+	if (mt_external_lock(mas->tree))
+		might_alloc(GFP_KERNEL);
+
 	trace_ma_write(TP_FCT, mas, 0, entry);
 #ifdef CONFIG_DEBUG_MAPLE_TREE
 	if (MAS_WARN_ON(mas, mas->index > mas->last))
@@ -5609,8 +5612,7 @@ void *mas_store(struct ma_state *mas, void *entry)
 		goto store;
 
 	mas_alloc_nodes(mas, GFP_NOWAIT);
-	if (mas_is_err(mas))
-		return NULL;
+	mas_nomem(mas, GFP_KERNEL | __GFP_NOFAIL);
 
 store:
 	mas_wr_store_entry(&wr_mas);
@@ -6351,7 +6353,7 @@ void *mas_erase(struct ma_state *mas)
 	/* Must reset to ensure spanning writes of last slot are detected */
 	mas_reset(mas);
 	mas_wr_preallocate(&wr_mas, NULL);
-	if (mas_nomem(mas, GFP_KERNEL)) {
+	if (mas_nomem(mas, GFP_KERNEL | __GFP_NOFAIL)) {
 		/* in case the range of entry changed when unlocked */
 		mas->index = mas->last = index;
 		goto write_retry;
@@ -6402,7 +6404,7 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp)
 	 * external lock with a non-blocking gfp in a low memory situation -
 	 * which would have triggered the first warning in this function.
 	 */
-	if (WARN_ON_ONCE(!mas->sheaf && !mas->alloc))
+	if (!mas->sheaf && !mas->alloc)
 		return false;
 
 	mas_reset(mas);
-- 
2.47.3


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