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From:   "Liam R. Howlett" <Liam.Howlett@oracle.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        stable@vger.kernel.org, jason.sim@samsung.com
Subject: [PATCH] maple_tree: Add GFP_KERNEL to allocations in mas_expected_entries()
Date:   Tue, 10 Oct 2023 10:17:37 -0400
Message-Id: <20231010141737.1592866-1-Liam.Howlett@oracle.com>
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Users complained about OOM errors during fork without triggering
compaction.  This can be fixed by modifying the flags used in
mas_expected_entries() so that the compaction will be triggered in low
memory situations.  Since mas_expected_entries() is only used during
fork, the extra argument does not need to be passed through.

Additionally, the testing in the maple tree fork testing needed to be
altered to use the correct locking type so that allocations would not
trigger sleeping and thus failures in the testing.  The additional
locking change requires rwsem support additions to the tools/ directory
through the use of pthreads pthread_rwlock_t.  With this change
test_maple_tree works in userspace, as a module, and in-kernel.

Users may notice that the system gave up early on attempting to start
new processes instead of attempting to reclaim memory.

Link: https://lkml.kernel.org/r/20230915093243epcms1p46fa00bbac1ab7b7dca94acb66c44c456@epcms1p4
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Cc: <stable@vger.kernel.org>
Cc: jason.sim@samsung.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 lib/maple_tree.c            |  2 +-
 lib/test_maple_tree.c       | 13 ++++++++----
 tools/include/linux/rwsem.h | 40 +++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 5 deletions(-)
 create mode 100644 tools/include/linux/rwsem.h

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 0e00a84e8e8f..bb24d84a4922 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5627,7 +5627,7 @@ int mas_expected_entries(struct ma_state *mas, unsigned long nr_entries)
 	/* Internal nodes */
 	nr_nodes += DIV_ROUND_UP(nr_nodes, nonleaf_cap);
 	/* Add working room for split (2 nodes) + new parents */
-	mas_node_count(mas, nr_nodes + 3);
+	mas_node_count_gfp(mas, nr_nodes + 3, GFP_KERNEL);
 
 	/* Detect if allocations run out */
 	mas->mas_flags |= MA_STATE_PREALLOC;
diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index 06959165e2f9..204743bc161c 100644
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -9,6 +9,7 @@
 
 #include <linux/maple_tree.h>
 #include <linux/module.h>
+#include <linux/rwsem.h>
 
 #define MTREE_ALLOC_MAX 0x2000000000000Ul
 #define CONFIG_MAPLE_SEARCH
@@ -2616,6 +2617,10 @@ static noinline void __init check_dup_gaps(struct maple_tree *mt,
 	void *tmp;
 	MA_STATE(mas, mt, 0, 0);
 	MA_STATE(newmas, &newmt, 0, 0);
+	struct rw_semaphore newmt_lock;
+
+	init_rwsem(&newmt_lock);
+	mt_set_external_lock(&newmt, &newmt_lock);
 
 	if (!zero_start)
 		i = 1;
@@ -2625,9 +2630,9 @@ static noinline void __init check_dup_gaps(struct maple_tree *mt,
 		mtree_store_range(mt, i*10, (i+1)*10 - gap,
 				  xa_mk_value(i), GFP_KERNEL);
 
-	mt_init_flags(&newmt, MT_FLAGS_ALLOC_RANGE);
+	mt_init_flags(&newmt, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN);
 	mt_set_non_kernel(99999);
-	mas_lock(&newmas);
+	down_write(&newmt_lock);
 	ret = mas_expected_entries(&newmas, nr_entries);
 	mt_set_non_kernel(0);
 	MT_BUG_ON(mt, ret != 0);
@@ -2640,9 +2645,9 @@ static noinline void __init check_dup_gaps(struct maple_tree *mt,
 	}
 	rcu_read_unlock();
 	mas_destroy(&newmas);
-	mas_unlock(&newmas);
 
-	mtree_destroy(&newmt);
+	__mt_destroy(&newmt);
+	up_write(&newmt_lock);
 }
 
 /* Duplicate many sizes of trees.  Mainly to test expected entry values */
diff --git a/tools/include/linux/rwsem.h b/tools/include/linux/rwsem.h
new file mode 100644
index 000000000000..83971b3cbfce
--- /dev/null
+++ b/tools/include/linux/rwsem.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+#ifndef _TOOLS__RWSEM_H
+#define _TOOLS__RWSEM_H
+
+#include <pthread.h>
+
+struct rw_semaphore {
+	pthread_rwlock_t lock;
+};
+
+static inline int init_rwsem(struct rw_semaphore *sem)
+{
+	return pthread_rwlock_init(&sem->lock, NULL);
+}
+
+static inline int exit_rwsem(struct rw_semaphore *sem)
+{
+	return pthread_rwlock_destroy(&sem->lock);
+}
+
+static inline int down_read(struct rw_semaphore *sem)
+{
+	return pthread_rwlock_rdlock(&sem->lock);
+}
+
+static inline int up_read(struct rw_semaphore *sem)
+{
+	return pthread_rwlock_unlock(&sem->lock);
+}
+
+static inline int down_write(struct rw_semaphore *sem)
+{
+	return pthread_rwlock_wrlock(&sem->lock);
+}
+
+static inline int up_write(struct rw_semaphore *sem)
+{
+	return pthread_rwlock_unlock(&sem->lock);
+}
+#endif /* _TOOLS_RWSEM_H */
-- 
2.40.1