If we make sure we grab a strong reference to each object as we dump it,
we can reduce the locks outside of our iterators to an rcu_read_lock.
This should prevent errors like:
[ 2138.371911] BUG: KASAN: use-after-free in per_file_stats+0x43/0x380 [i915]
[ 2138.371924] Read of size 8 at addr ffff888223651000 by task cat/8293
[ 2138.371947] CPU: 0 PID: 8293 Comm: cat Not tainted 5.3.0-rc6-CI-Custom_4352+
#1
[ 2138.371953] Hardware name: To Be Filled By O.E.M. To Be Filled By
O.E.M./J4205-ITX, BIOS P1.40 07/14/2017
[ 2138.371959] Call Trace:
[ 2138.371974] dump_stack+0x7c/0xbb
[ 2138.372099] ? per_file_stats+0x43/0x380 [i915]
[ 2138.372108] print_address_description+0x73/0x3a0
[ 2138.372231] ? per_file_stats+0x43/0x380 [i915]
[ 2138.372352] ? per_file_stats+0x43/0x380 [i915]
[ 2138.372362] __kasan_report+0x14e/0x192
[ 2138.372489] ? per_file_stats+0x43/0x380 [i915]
[ 2138.372502] kasan_report+0xe/0x20
[ 2138.372625] per_file_stats+0x43/0x380 [i915]
[ 2138.372751] ? i915_panel_show+0x110/0x110 [i915]
[ 2138.372761] idr_for_each+0xa7/0x160
[ 2138.372773] ? idr_get_next_ul+0x110/0x110
[ 2138.372782] ? do_raw_spin_lock+0x10a/0x1d0
[ 2138.372923] print_context_stats+0x264/0x510 [i915]
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
drivers/gpu/drm/i915/i915_debugfs.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
b/drivers/gpu/drm/i915/i915_debugfs.c
index 9798f27a697a..708855e051b5 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -237,6 +237,9 @@ static int per_file_stats(int id, void *ptr, void *data)
struct file_stats *stats = data;
struct i915_vma *vma;
+ if (!kref_get_unless_zero(&obj->base.refcount))
+ return 0;
+
stats->count++;
stats->total += obj->base.size;
if (!atomic_read(&obj->bind_count))
@@ -284,6 +287,7 @@ static int per_file_stats(int id, void *ptr, void *data)
}
spin_unlock(&obj->vma.lock);
+ i915_gem_object_put(obj);
return 0;
}
@@ -313,10 +317,12 @@ static void print_context_stats(struct seq_file *m,
i915_gem_context_lock_engines(ctx), it) {
intel_context_lock_pinned(ce);
if (intel_context_is_pinned(ce)) {
+ rcu_read_lock();
if (ce->state)
per_file_stats(0,
ce->state->obj, &kstats);
per_file_stats(0, ce->ring->vma->obj, &kstats);
+ rcu_read_unlock();
}
intel_context_unlock_pinned(ce);
}
@@ -328,9 +334,9 @@ static void print_context_stats(struct seq_file *m,
struct task_struct *task;
char name[80];
- spin_lock(&file->table_lock);
+ rcu_read_lock();
idr_for_each(&file->object_idr, per_file_stats, &stats);
- spin_unlock(&file->table_lock);
+ rcu_read_unlock();
rcu_read_lock();
task = pid_task(ctx->pid ?: file->pid, PIDTYPE_PID);
--
2.23.0
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