Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 10 Sep 2019 10:14:53 +0200 | Subject | Re: [PATCH] net/mlx5: reduce stack usage in FW tracer |
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On Mon, Sep 9, 2019 at 11:53 PM Saeed Mahameed <saeedm@mellanox.com> wrote: > On Mon, 2019-09-09 at 22:18 +0200, Arnd Bergmann wrote:
> > To do this right, a better approach may be to just rely on ftrace, > > storing > > the (pointer to the) format string and the arguments in the buffer > > without > > creating a string. Would that be an option here? > > I am not sure how this would work, since the format parameters can > changes depending on the FW string and the specific traces.
Ah, so the format string comes from the firmware? I didn't look at the code in enough detail to understand why it's done like this, only enough to notice that it's rather unusual.
Possibly trace_mlx5_fw might still get away with copying the format string and the arguments, leaving the snprintf() to the time we read the buffer, but I don't know enough about ftrace to be sure that would actually work, and you'd need to duplicate it in mlx5_devlink_fmsg_fill_trace().
> > A more minimal approach might be to move what is now the on-stack > > buffer into the mlx5_fw_tracer function. I see that you already store > > a copy of the string in there from mlx5_fw_tracer_save_trace(), > > which conveniently also holds a mutex already that protects > > it from concurrent access. > > > > This sounds plausible. > > So for now let's do this or the noinline approach, Please let me know > which one do you prefer, if it is the mutex protected buffer, i can do > it myself. > > I will open an internal task and discussion then address your valuable > points in a future submission, since we already in rc8 I don't want to > take the risk now.
Yes, that sounds like a good plan. If you can't avoid the snprintf entirely, then the mutex protected buffer should be helpful, and also avoid a strncpy() along with the stack buffer.
Arnd
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