Re: [PATCH v2 tip/perf/core 3/5] fs: add back RCU-delayed freeing of FMODE_BACKING file

[Christian Brauner]

On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote:
> 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING
> files to direct freeing as back then there were no use cases requiring
> RCU protected access to such files.
> 
> Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to
> have a guarantee that struct file memory is not going to be freed from
> under us during speculative check. So add back RCU-delayed freeing
> logic.
> 
> We use headless kfree_rcu_mightsleep() variant, as file_free() is only
> called for FMODE_BACKING files in might_sleep() context.
> 
> Suggested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: Amir Goldstein <amir73il@xxxxxxxxx>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---

Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>