On 8/4/2018 10:47 PM, Rob Clark wrote:
On Thu, Jul 12, 2018 at 3:48 PM Chris Wilson chris@chris-wilson.co.uk wrote:
Quoting Jordan Crouse (2018-07-12 19:59:25)
Do a bit of cleanup to prepare for upcoming changes to pass the hanging task comm and cmdline to the crash dump function.
Signed-off-by: Jordan Crouse jcrouse@codeaurora.org
drivers/gpu/drm/msm/msm_gpu.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c index 1c09acfb4028..2ca354047250 100644 --- a/drivers/gpu/drm/msm/msm_gpu.c +++ b/drivers/gpu/drm/msm/msm_gpu.c @@ -314,6 +314,7 @@ static void recover_worker(struct work_struct *work) struct msm_drm_private *priv = dev->dev_private; struct msm_gem_submit *submit; struct msm_ringbuffer *cur_ring = gpu->funcs->active_ring(gpu);
char *comm = NULL, *cmd = NULL; int i; mutex_lock(&dev->struct_mutex);@@ -327,7 +328,7 @@ static void recover_worker(struct work_struct *work) rcu_read_lock(); task = pid_task(submit->pid, PIDTYPE_PID); if (task) {
char *cmd;
comm = kstrdup(task->comm, GFP_KERNEL);Under rcu_read_lock(), GFP_KERNEL is not allowed, you need GFP_NOWAIT or some such (or grab a reference to the pid and drop rcu then GFP_KERNEL).
I started looking at a similar issue w/ our use of kstrdup_quotable_cmdline() under rcu_read_lock().. I *guess* I hadn't noticed it before due to different RCU kconfig?
I can use GFP_ATOMIC, and I can fix kstrdup_quotable_cmdline() to actually use gfp flags passed in for kmalloc() (and similar bug in kstrdup_quotable_file()).. but get_cmdline() still grabs mmap_sem which complains under rcu_read_lock()..
is there any way to ensure the tast_struct sticks around long enough to get it's cmdline without holding rcu_read_lock()? I couldn't find any refcnt'ing on task_struct itself, which makes this seem a bit unsolveable :-/
I have been seeing similar issues on my downstream setup and was looking into fixing this actively. Here is a way to have the task stay afloat and revert to GFP_KERNEL https://patchwork.freedesktop.org/patch/256397/ Please review... I tried this out and it does work.
BR,
-R
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