maple_tree: add GFP_KERNEL to allocations in mas_expected_entries()

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 two test_maple_tree test cases and one benchmark test
were altered to use the correct locking type so that allocations would not
trigger sleeping and thus fail.  Testing was completed with lockdep atomic
sleep detection.

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
Link: https://lkml.kernel.org/r/20231012155233.2272446-1-Liam.Howlett@oracle.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: <jason.sim@samsung.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 40 insertions, 0 deletions

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 */