linux-kernel - [PATCH 4.19 14/67] drm/msm: Fix task dump in gpu recovery

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Date:   Thu, 20 Dec 2018 10:18:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sharat Masetty <smasetty@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 14/67] drm/msm: Fix task dump in gpu recovery

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 482f96324a4e08818db7d75bb12beaaea6c9561d ]

The current recovery code gets a pointer to the task struct and does a
few things all within the rcu_read_lock. This puts constraints on the
types of gfp flags that can be used within the rcu lock. This patch
instead gets a reference to the task within the rcu lock and releases
the lock immediately, this way the task stays afloat until we need it and
we also get to use the desired gfp flags.

Signed-off-by: Sharat Masetty <smasetty@...eaurora.org>
Signed-off-by: Rob Clark <robdclark@...il.com>
Signed-off-by: Sean Paul <seanpaul@...omium.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/msm/msm_gpu.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index 46e6b82f7b66..52a2146dc1f2 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -425,10 +425,9 @@ static void recover_worker(struct work_struct *work)
 	if (submit) {
 		struct task_struct *task;
 
-		rcu_read_lock();
-		task = pid_task(submit->pid, PIDTYPE_PID);
+		task = get_pid_task(submit->pid, PIDTYPE_PID);
 		if (task) {
-			comm = kstrdup(task->comm, GFP_ATOMIC);
+			comm = kstrdup(task->comm, GFP_KERNEL);
 
 			/*
 			 * So slightly annoying, in other paths like
@@ -441,10 +440,10 @@ static void recover_worker(struct work_struct *work)
 			 * about the submit going away.
 			 */
 			mutex_unlock(&dev->struct_mutex);
-			cmd = kstrdup_quotable_cmdline(task, GFP_ATOMIC);
+			cmd = kstrdup_quotable_cmdline(task, GFP_KERNEL);
+			put_task_struct(task);
 			mutex_lock(&dev->struct_mutex);
 		}
-		rcu_read_unlock();
 
 		if (comm && cmd) {
 			dev_err(dev->dev, "%s: offending task: %s (%s)\n",
-- 
2.19.1