selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 124 insertions, 0 deletions

diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c
new file mode 100644
index 000000000..9e5d662cd
--- /dev/null
+++ b/drivers/dma-buf/sync_debug.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Sync File validation framework and debug information
+ *
+ * Copyright (C) 2012 Google, Inc.
+ */
+
+#include <linux/debugfs.h>
+#include "sync_debug.h"
+
+static struct dentry *dbgfs;
+
+static LIST_HEAD(sync_timeline_list_head);
+static DEFINE_SPINLOCK(sync_timeline_list_lock);
+
+void sync_timeline_debug_add(struct sync_timeline *obj)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&sync_timeline_list_lock, flags);
+	list_add_tail(&obj->sync_timeline_list, &sync_timeline_list_head);
+	spin_unlock_irqrestore(&sync_timeline_list_lock, flags);
+}
+
+void sync_timeline_debug_remove(struct sync_timeline *obj)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&sync_timeline_list_lock, flags);
+	list_del(&obj->sync_timeline_list);
+	spin_unlock_irqrestore(&sync_timeline_list_lock, flags);
+}
+
+static const char *sync_status_str(int status)
+{
+	if (status < 0)
+		return "error";
+
+	if (status > 0)
+		return "signaled";
+
+	return "active";
+}
+
+static void sync_print_fence(struct seq_file *s,
+			     struct dma_fence *fence, bool show)
+{
+	struct sync_timeline *parent = dma_fence_parent(fence);
+	int status;
+
+	status = dma_fence_get_status_locked(fence);
+
+	seq_printf(s, "  %s%sfence %s",
+		   show ? parent->name : "",
+		   show ? "_" : "",
+		   sync_status_str(status));
+
+	if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags)) {
+		struct timespec64 ts64 =
+			ktime_to_timespec64(fence->timestamp);
+
+		seq_printf(s, "@%ptSp", &ts64);
+	}
+
+	seq_printf(s, ": %lld", fence->seqno);
+	seq_printf(s, " / %d", parent->value);
+	seq_putc(s, '\n');
+}
+
+static void sync_print_obj(struct seq_file *s, struct sync_timeline *obj)
+{
+	struct list_head *pos;
+
+	seq_printf(s, "%s: %d\n", obj->name, obj->value);
+
+	spin_lock(&obj->lock); /* Caller already disabled IRQ. */
+	list_for_each(pos, &obj->pt_list) {
+		struct sync_pt *pt = container_of(pos, struct sync_pt, link);
+		sync_print_fence(s, &pt->base, false);
+	}
+	spin_unlock(&obj->lock);
+}
+
+static int sync_info_debugfs_show(struct seq_file *s, void *unused)
+{
+	struct list_head *pos;
+
+	seq_puts(s, "objs:\n--------------\n");
+
+	spin_lock_irq(&sync_timeline_list_lock);
+	list_for_each(pos, &sync_timeline_list_head) {
+		struct sync_timeline *obj =
+			container_of(pos, struct sync_timeline,
+				     sync_timeline_list);
+
+		sync_print_obj(s, obj);
+		seq_putc(s, '\n');
+	}
+	spin_unlock_irq(&sync_timeline_list_lock);
+
+	seq_puts(s, "fences:\n--------------\n");
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(sync_info_debugfs);
+
+static __init int sync_debugfs_init(void)
+{
+	dbgfs = debugfs_create_dir("sync", NULL);
+
+	/*
+	 * The debugfs files won't ever get removed and thus, there is
+	 * no need to protect it against removal races. The use of
+	 * debugfs_create_file_unsafe() is actually safe here.
+	 */
+	debugfs_create_file_unsafe("info", 0444, dbgfs, NULL,
+				   &sync_info_debugfs_fops);
+	debugfs_create_file_unsafe("sw_sync", 0644, dbgfs, NULL,
+				   &sw_sync_debugfs_fops);
+
+	return 0;
+}
+late_initcall(sync_debugfs_init);