[PATCH AUTOSEL 6.6 30/66] media: rkvdec: Initialize the m2m context before the controls

Sasha Levin
2025-06-01T23:38:57Z

From: Nicolas Dufresne <nicolas.dufresne@collabora.com>

[ Upstream commit d43d7db3c8a1868dcbc6cb8de90a3cdf309d6cbb ]

Setting up the control handler calls into .s_ctrl ops. While validating
the controls the ops may need to access some of the context state, which
could lead to a crash if not properly initialized.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

Now let me analyze the specific changes proposed in the commit: ##
Analysis **YES** This commit should be backported to stable kernel
trees. Here's my extensive analysis: ### Core Issue Analysis The commit
addresses a critical initialization order bug that can lead to crashes.
The problem occurs in the `rkvdec_open()` function at lines 822-830 in
the current code: 1. **Current problematic order:** - Line 822:
`rkvdec_init_ctrls(ctx)` is called first - Line 826-830:
`v4l2_m2m_ctx_init()` is called second 2. **The problem:** According to
the commit message and my analysis of the kernel documentation,
`v4l2_ctrl_handler_setup()` (called inside `rkvdec_init_ctrls()`) calls
`.s_ctrl` for all controls unconditionally to initialize hardware to
default values. The `.s_ctrl` handlers may need to access the m2m
context state, but if the m2m context (`ctx->fh.m2m_ctx`) isn't
initialized yet, this can cause a crash or undefined behavior. ### Code
Changes Analysis The fix is minimal and surgical: - **Lines moved:** The
initialization order is swapped - m2m context initialization moves
before control handler setup - **Error handling updated:** The error
handling paths are correctly updated to match the new initialization
order - **No functional changes:** The fix doesn't change driver
functionality, only initialization sequence ### Why This Should Be
Backported 1. **Fixes a real crash bug:** This addresses a potential
crash scenario that affects users 2. **Small and contained:** The change
is minimal - just reordering initialization and updating error paths 3.
**Low regression risk:** Moving m2m init before control init is safer
since m2m context doesn't depend on controls, but controls may depend on
m2m context 4. **Follows established patterns:** Similar commit #2 in
the historical examples shows a "YES" backport for proper initialization
order in V4L2 drivers 5. **Critical subsystem:** Media drivers crashing
can affect user applications ### Comparison with Historical Commits -
**Similar to commit #2 (YES):** Also fixes initialization order in V4L2
media driver to prevent crashes - **Similar to commit #4 (YES):** Media
driver fix that's low-risk and contained - **Unlike commits #1, #3, #5
(NO):** This actually fixes a bug rather than just cleanup/code style
improvements ### Stable Tree Criteria Met ✅ **Important bugfix:**
Prevents crashes ✅ **Minimal risk:** Simple reordering with no side
effects ✅ **Small change:** Only affects initialization sequence ✅ **No
architectural changes:** Pure bug fix ✅ **Confined to subsystem:** Only
affects rkvdec driver The fix follows the stable tree rules perfectly -
it's an important crash prevention fix with minimal regression risk,
making it an ideal backport candidate.

drivers/staging/media/rkvdec/rkvdec.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/media/rkvdec/rkvdec.c b/drivers/staging/media/rkvdec/rkvdec.c
index ac398b5a97360..838ff0ee0bbb4 100644
--- a/drivers/staging/media/rkvdec/rkvdec.c
+++ b/drivers/staging/media/rkvdec/rkvdec.c
@@ -821,24 +821,24 @@ static int rkvdec_open(struct file *filp)
rkvdec_reset_decoded_fmt(ctx);
v4l2_fh_init(&ctx->fh, video_devdata(filp));

- ret = rkvdec_init_ctrls(ctx);
- if (ret)
- goto err_free_ctx;
-
ctx->fh.m2m_ctx = v4l2_m2m_ctx_init(rkvdec->m2m_dev, ctx,
rkvdec_queue_init);
if (IS_ERR(ctx->fh.m2m_ctx)) {
ret = PTR_ERR(ctx->fh.m2m_ctx);
- goto err_cleanup_ctrls;
+ goto err_free_ctx;
}

+ ret = rkvdec_init_ctrls(ctx);
+ if (ret)
+ goto err_cleanup_m2m_ctx;
+
filp->private_data = &ctx->fh;
v4l2_fh_add(&ctx->fh);

return 0;

-err_cleanup_ctrls:
- v4l2_ctrl_handler_free(&ctx->ctrl_hdl);
+err_cleanup_m2m_ctx:
+ v4l2_m2m_ctx_release(ctx->fh.m2m_ctx);

err_free_ctx:
kfree(ctx);
--
2.39.5