On 23/12/2023 17:43, Tuo Li wrote:
Accesses to ctx->s_frame.width and ctx->s_frame.height should be protectedOther places setting parts of s_frame, like fimc_capture_try_format() or
by the lock fimc->lock to guarantee that width and height are consistent.
Here is an example in fimc_subdev_get_fmt():
struct fimc_frame *ff = &ctx->s_frame; // Alias
mutex_lock(&fimc->lock);
mf->width = ff->width;
mf->height = ff->height;
However, ctx->s_frame.width and ctx->s_frame.height are accessed without
holding the lock fimc->lock in fimc_subdev_set_fmt():
mf->width = ctx->s_frame.width;
mf->height = ctx->s_frame.height;
fimc_capture_try_selection(), do not have mutex.
And thus a harmful data race can occur, which can make ctx->s_frame.widthHarmful how?
inconsistent with ctx->s_frame.height, if ctx->s_frame.height is updatedYou wrote long four paragraphs which have basically almost zero relevant
right after ctx->s_frame.width is accessed by another thread.
This possible bug is found by an experimental static analysis tool
developed by our team, BassCheck[1]. This tool analyzes the locking APIs
to extract function pairs that can be concurrently executed, and then
analyzes the instructions in the paired functions to identify possible
concurrency bugs including data races and atomicity violations. The above
possible bug is reported when our tool analyzes the source code of
Linux 6.2.
To fix this possible data race, the lock operation mutex_lock(&fimc->lock)
is moved to the front of the accesses to these two variables. With this
patch applied, our tool no longer reports the bug, with the kernel
configuration allyesconfig for x86_64. Due to the lack of associated
hardware, we cannot test the patch in runtime testing, and just verify it
according to the code logic.
information, whether this locking is needed or not. Your bass
description is not relevant... or actually making things worse because I
am certain you are fixing it just to fix your report, not to fix real issue.
[1] https://sites.google.com/view/basscheck/Instead provide the report.
Fixes: 88fa8311ee36 ("[media] s5p-fimc: Add support for ISP Writeback ...")Run checkpatch, you will see the warning.
Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: BassCheck <bass@xxxxxxxxxxx>
Best regards,Sincerely,
Krzysztof