linux-kernel - [PATCH 4/7] drm/etnaviv: protect whole iommuv2 ctx alloc func under global mutex

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Message-ID: <20250816074757.2559055-5-uwu@icenowy.me>
Date: Sat, 16 Aug 2025 15:47:54 +0800
From: Icenowy Zheng <uwu@...nowy.me>
To: Drew Fustini <fustini@...nel.org>,
	Guo Ren <guoren@...nel.org>,
	Fu Wei <wefu@...hat.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Russell King <linux+etnaviv@...linux.org.uk>,
	Christian Gmeiner <christian.gmeiner@...il.com>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	etnaviv@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org,
	Icenowy Zheng <uwu@...nowy.me>
Subject: [PATCH 4/7] drm/etnaviv: protect whole iommuv2 ctx alloc func under global mutex

As we are forced to use a global shared context on some
PTA-equipped-but-broken GPUs, the fine-grained mutex locking in the
current implemtnation of etnaviv_iommuv2_context_alloc() won't be
meaningful any more.

Make the whole function to be protected by the global lock, in order to
prevent reentrance when allocating global shared context.

Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
---
 drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c b/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
index d664ae29ae209..5654a604c70cf 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
@@ -272,20 +272,18 @@ etnaviv_iommuv2_context_alloc(struct etnaviv_iommu_global *global)
 	struct etnaviv_iommuv2_context *v2_context;
 	struct etnaviv_iommu_context *context;
 
+	mutex_lock(&global->lock);
+
 	v2_context = vzalloc(sizeof(*v2_context));
 	if (!v2_context)
-		return NULL;
+		goto out_mutex_unlock;
 
-	mutex_lock(&global->lock);
 	v2_context->id = find_first_zero_bit(global->v2.pta_alloc,
 					     ETNAVIV_PTA_ENTRIES);
-	if (v2_context->id < ETNAVIV_PTA_ENTRIES) {
+	if (v2_context->id < ETNAVIV_PTA_ENTRIES)
 		set_bit(v2_context->id, global->v2.pta_alloc);
-	} else {
-		mutex_unlock(&global->lock);
+	else
 		goto out_free;
-	}
-	mutex_unlock(&global->lock);
 
 	v2_context->mtlb_cpu = dma_alloc_wc(global->dev, SZ_4K,
 					    &v2_context->mtlb_dma, GFP_KERNEL);
@@ -304,11 +302,14 @@ etnaviv_iommuv2_context_alloc(struct etnaviv_iommu_global *global)
 	INIT_LIST_HEAD(&context->mappings);
 	drm_mm_init(&context->mm, SZ_4K, (u64)SZ_1G * 4 - SZ_4K);
 
+	mutex_unlock(&global->lock);
 	return context;
 
 out_free_id:
 	clear_bit(v2_context->id, global->v2.pta_alloc);
 out_free:
 	vfree(v2_context);
+out_mutex_unlock:
+	mutex_unlock(&global->lock);
 	return NULL;
 }
-- 
2.50.1