From: Rob Clark robdclark@chromium.org
[ Upstream commit f681c2aa8676a890eacc84044717ab0fd26e058f ]
put_unused_fd() doesn't free the installed file, if we've already done fd_install(). So we need to also free the sync_file.
Signed-off-by: Rob Clark robdclark@chromium.org Patchwork: https://patchwork.freedesktop.org/patch/653583/ Signed-off-by: Rob Clark robin.clark@oss.qualcomm.com Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my analysis, **YES**, this commit should be backported to stable kernel trees.
## Extensive Explanation:
This commit fixes a **resource leak** in the MSM DRM driver's submit error path, which is a clear bug that affects users and meets the stable tree criteria.
### The Bug:
Looking at the code changes in `msm_gem_submit.c`:
1. **Before the fix**: When an error occurs after `fd_install()` has been called (line 865 in the context), the error path only calls `put_unused_fd(out_fence_fd)` at line 895-896.
2. **The problem**: As noted in the commit message, `put_unused_fd()` doesn't free the installed file if `fd_install()` has already been executed. The `sync_file` structure created by `sync_file_create()` (line 861) contains a file reference that needs to be released with `fput()`.
3. **The fix**: The patch adds proper cleanup by: - Moving `sync_file` declaration to function scope (line 661) - Adding proper cleanup in the error path (lines 895-898) that calls both `put_unused_fd()` AND `fput(sync_file->file)` when needed
### Why This Is a Good Backport Candidate:
1. **Clear Bug Fix**: This fixes a resource leak that can accumulate over time as applications hit error conditions during fence submission.
2. **Small and Contained**: The fix is minimal - just 5 lines of actual code changes that properly clean up resources.
3. **No Architectural Changes**: This doesn't introduce new features or change any APIs - it simply fixes error handling.
4. **Similar to Previous Backported Fixes**: Looking at similar commit #3 ("drm/msm: Fix submit error-path leaks") which was marked for backporting, this follows the same pattern of fixing resource leaks in error paths.
5. **Low Risk**: The change only affects error paths and adds proper cleanup that was missing. It cannot break the normal success path.
6. **Documentation Confirms**: The sync_file.c documentation (line 62-63) explicitly states that sync_files should be released with `fput(sync_file->file)`, confirming this is the correct fix.
### Pattern Analysis:
Comparing with the similar commits provided: - Similar commits #1, #2, and #4 were NOT backported (they were general code improvements or non-critical changes) - Similar commits #3 and #5 WERE backported (they fixed actual resource leaks or initialization failures)
This commit clearly falls into the same category as #3 and #5 - fixing an actual resource leak that can impact system stability over time.
The leak occurs whenever: 1. A sync_file is successfully created 2. fd_install() succeeds 3. But then a subsequent error occurs before the submit completes
Without this fix, each occurrence leaks a file descriptor and associated kernel memory, which could eventually exhaust resources in systems with heavy GPU usage that encounter errors.
drivers/gpu/drm/msm/msm_gem_submit.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c index 937c1f5d88cbb..4b3a8ee8e278f 100644 --- a/drivers/gpu/drm/msm/msm_gem_submit.c +++ b/drivers/gpu/drm/msm/msm_gem_submit.c @@ -667,6 +667,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data, struct msm_ringbuffer *ring; struct msm_submit_post_dep *post_deps = NULL; struct drm_syncobj **syncobjs_to_reset = NULL; + struct sync_file *sync_file = NULL; int out_fence_fd = -1; unsigned i; int ret; @@ -877,7 +878,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data, }
if (ret == 0 && args->flags & MSM_SUBMIT_FENCE_FD_OUT) { - struct sync_file *sync_file = sync_file_create(submit->user_fence); + sync_file = sync_file_create(submit->user_fence); if (!sync_file) { ret = -ENOMEM; } else { @@ -911,8 +912,11 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data, out_unlock: mutex_unlock(&queue->lock); out_post_unlock: - if (ret && (out_fence_fd >= 0)) + if (ret && (out_fence_fd >= 0)) { put_unused_fd(out_fence_fd); + if (sync_file) + fput(sync_file->file); + }
if (!IS_ERR_OR_NULL(submit)) { msm_gem_submit_put(submit);