Hi,std::memory_order
media: v4l2-mem2mem: fix mem order in last bufmem order ? Did you mean call order ?
Access to those 3 booleans you mentioned later.
Le dimanche 11 février 2024 à 02:04 +0800, Hsia-Jun Li a écrit :
From: "Hsia-Jun(Randy) Li" <randy.li@xxxxxxxxxxxxx>protection When ? ~~
The has_stopped property in struct v4l2_m2m_ctx is operated
without a lock protecction. Then the userspace calls to
v4l2_m2m_encoder_cmd()/v4l2_m2m_decoder_cmd() may lead toAs there is no locking, there is no critical section, perhaps a better phrasing
a critical section issue.
could help.
Signed-off-by: Hsia-Jun(Randy) Li <randy.li@xxxxxxxxxxxxx>While it most likely fix the issue while testing, since userspace most likely
---
drivers/media/v4l2-core/v4l2-mem2mem.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
index 75517134a5e9..f1de71031e02 100644
--- a/drivers/media/v4l2-core/v4l2-mem2mem.c
+++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
@@ -635,9 +635,9 @@ void v4l2_m2m_last_buffer_done(struct v4l2_m2m_ctx *m2m_ctx,
struct vb2_v4l2_buffer *vbuf)
{
vbuf->flags |= V4L2_BUF_FLAG_LAST;
- vb2_buffer_done(&vbuf->vb2_buf, VB2_BUF_STATE_DONE);
-
v4l2_m2m_mark_stopped(m2m_ctx);
+
+ vb2_buffer_done(&vbuf->vb2_buf, VB2_BUF_STATE_DONE);
polls on that queue and don't touch the driver until the poll was signalled, I
strongly believe this is insufficient. When I look at vicodec and wave5, they
both add a layer of locking on top of the mem2mem framework to fix this issue.
I think this is unfortunate, but v4l2_m2m_mark_stopped() is backed by 3 booleansI tend to not introduce more locks here. There is a spinlock in m2m_ctx which is a pain in the ass, something we could reuse it to save our CPU but it just can't be access.
accessed in many places that aren't in any known atomic context. I think it
would be nice to remove the spurious locking in drivers and try and fix this
issue in the framework itself.
Nicolas
}
EXPORT_SYMBOL_GPL(v4l2_m2m_last_buffer_done);