From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 165C84418DB; Wed, 6 May 2026 12:16:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778069802; cv=none; b=iyrCIqZ9znOPk6BqavZt9Nx/Dg6LgGCF1G3ukvRK5TxDAvn/fyXWaTKAlVrd1PwvqdIo0/ItS2diFZLU8qRXT/tWg9GYBxMG6HI57P3tBoGDg4To9Cwce54TaQLe9jU4tO4CoRYeMYJHLoK52V9H+5ZizSyC11qkV24WSPQ1TTY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778069802; c=relaxed/simple; bh=u1rbbnIoyFZA7O2vs7QHol/yHibz7ircmGOOnRxEjGA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=bY+7txzvb0AfiaQhBb6/fwa7D7YJlU3NssdMoeD7qZ0R8GlRwNYIsKeXBlNqAK81qpjULr0ZcOeDuNP1NBzxaK3li2Arf4tKGOUcJGbggJncPgpaieVv0XKg2kny8gGUTmk1fgpU+sWTwJ0mWHT1AqIvI0yEn4pvEGmBB21+dtY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=HwIiRzUq; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="HwIiRzUq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1778069799; bh=u1rbbnIoyFZA7O2vs7QHol/yHibz7ircmGOOnRxEjGA=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=HwIiRzUqisePGYSP+oQv8nut2BrQ2Y8Yz8rFZyvpXSXIu7PXyeQTv249ZYry8t5FR fFHvXPH6osctGucWoC4Py5gh+56RV9cb2cKqXg+xZxMlxkr1BU1nMaLmEF0dY/9bom 8U6gtSxzpKQD4MJedEhlwrdzVZ9xguxercMdIKl5K/scxHlpTCCqd7FaDDtQBgib3s vrDk7euO9rvVmNaF3F94HWrpkFy9aQLBdySDTuFadoQ9f5BoQkUx07lfZBLQNclaNM bKNNVU/J5Dug5BJUUW8lL+kKmty/lAwn86wPo/uyg5ZwUoFWMMniXkivncb7UWOAzh uQPcjpPDJ4r0w== Received: from [100.64.0.11] (unknown [100.64.0.11]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by bali.collaboradmins.com (Postfix) with ESMTPSA id 94F7917E1537; Wed, 6 May 2026 14:16:38 +0200 (CEST) From: Boris Brezillon Date: Wed, 06 May 2026 14:16:27 +0200 Subject: [PATCH 2/3] drm/gem: Fix a race between drm_gem_lru_scan() and drm_gem_object_release() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260506-panthor-shrinker-fixes-v1-2-e7721526de96@collabora.com> References: <20260506-panthor-shrinker-fixes-v1-0-e7721526de96@collabora.com> In-Reply-To: <20260506-panthor-shrinker-fixes-v1-0-e7721526de96@collabora.com> To: Steven Price , Liviu Dudau , Boris Brezillon , Dmitry Osipenko Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Akash Goel , Chia-I Wu , Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Jessica Zhang , Sean Paul , Marijn Suijten , linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1778069796; l=2777; i=boris.brezillon@collabora.com; s=20260429; h=from:subject:message-id; bh=u1rbbnIoyFZA7O2vs7QHol/yHibz7ircmGOOnRxEjGA=; b=0Vn0g7A6fEq54VBM8lGGCLNX9mHH+iAkL1OkGKe/jCH9w71OWroJV8R46OeF5EN1tdfdBhZwI cmjDTvLf01KDnH2rNOTeUgKqGCKEDTXPmK0yMv53DqAjtz8gkdpAlyR X-Developer-Key: i=boris.brezillon@collabora.com; a=ed25519; pk=eN+ORdOgQY7d5U+0kA8h5bf67XdD8bhKbjD/TCHexSY= The following race can currently happen: | Thread 0 in `drm_gem_lru_scan` | Thread 1 in `drm_gem_object_release` | | - | - | | move obj1 with refcount==0 to `still_in_lru` | | | move obj2 with refcount!=0 to `still_in_lru` | | | mutex_unlock | | | shrink obj2 | | | | lru = obj1->lru; // `still_in_lru` | | mutex_lock | | | move obj1 back to the original lru | | | mutex_unlock | | | return | | | | dereference `still_in_lru` | Move the drm_gem_lru_move_tail_locked() after the kref_get_unless_zero() check so that we don't end up with a vanishing LRU when we hit drm_gem_object_release(). We also need to remove the skipped object from its LRU, otherwise we'll keep hitting it on subsequent loop iterations until it's actually removed from the list in the drm_gem_release(). Fixes: e7c2af13f811 ("drm/gem: Add LRU/shrinker helper") Reported-by: Chia-I Wu Closes: https://gitlab.freedesktop.org/panfrost/linux/-/work_items/86 Signed-off-by: Boris Brezillon Reviewed-by: Chia-I Wu --- drivers/gpu/drm/drm_gem.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index fca42949eb2b..97cf63de0112 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -1660,15 +1660,19 @@ drm_gem_lru_scan(struct drm_gem_lru *lru, if (!obj) break; - drm_gem_lru_move_tail_locked(&still_in_lru, obj); - /* * If it's in the process of being freed, gem_object->free() - * may be blocked on lock waiting to remove it. So just - * skip it. + * may be blocked on lock waiting to remove it. So just remove + * it from its current LRU and skip it. */ - if (!kref_get_unless_zero(&obj->refcount)) + if (!kref_get_unless_zero(&obj->refcount)) { + if (obj->lru) + drm_gem_lru_remove_locked(obj); + continue; + } + + drm_gem_lru_move_tail_locked(&still_in_lru, obj); /* * Now that we own a reference, we can drop the lock for the -- 2.54.0