Re: [PATCH] interconnect: Don't access req_list while it's being manipulated

[Greg KH]

On Tue, Mar 05, 2024 at 02:56:52PM -0800, Mike Tipton wrote:
> The icc_lock mutex was split into separate icc_lock and icc_bw_lock
> mutexes in [1] to avoid lockdep splats. However, this didn't adequately
> protect access to icc_node::req_list.
> 
> The icc_set_bw() function will eventually iterate over req_list while
> only holding icc_bw_lock, but req_list can be modified while only
> holding icc_lock. This causes races between icc_set_bw(), of_icc_get(),
> and icc_put().
> 
> Example A:
> 
>   CPU0                               CPU1
>   ----                               ----
>   icc_set_bw(path_a)
>     mutex_lock(&icc_bw_lock);
>                                      icc_put(path_b)
>                                        mutex_lock(&icc_lock);
>     aggregate_requests()
>       hlist_for_each_entry(r, ...
>                                        hlist_del(...
>         <r = invalid pointer>
> 
> Example B:
> 
>   CPU0                               CPU1
>   ----                               ----
>   icc_set_bw(path_a)
>     mutex_lock(&icc_bw_lock);
>                                      path_b = of_icc_get()
>                                        of_icc_get_by_index()
>                                          mutex_lock(&icc_lock);
>                                          path_find()
>                                            path_init()
>     aggregate_requests()
>       hlist_for_each_entry(r, ...
>                                              hlist_add_head(...
>         <r = invalid pointer>
> 
> Fix this by ensuring icc_bw_lock is always held before manipulating
> icc_node::req_list. The additional places icc_bw_lock is held don't
> perform any memory allocations, so we should still be safe from the
> original lockdep splats that motivated the separate locks.
> 
> [1] commit af42269c3523 ("interconnect: Fix locking for runpm vs reclaim")
> 
> Signed-off-by: Mike Tipton <quic_mdtipton@xxxxxxxxxxx>
> Fixes: af42269c3523 ("interconnect: Fix locking for runpm vs reclaim")
> ---
>  drivers/interconnect/core.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
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created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
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