Re: [PATCH 1/9] w1: use the bus mutex for the "rw" file

[Krzysztof Kozlowski]

On 27/10/2026 17:04, Greg Kroah-Hartman wrote:
> From: Josef Bacik <josef@xxxxxxxxxxxxxx>
> 
> Commit b02f8bede217 ("W1: split master mutex to avoid deadlocks.") gave
> the bus a mutex of its own, because the lock which protects the list of
> slaves is held while a slave is removed, which waits for the sysfs
> callbacks of the slave, so these must not take it.  It converted all the
> slave drivers, but not the "rw" file of the default family in w1.c,
> which still takes the mutex of the master to talk on the bus.  That has
> two consequences:
> 
> - A deadlock.  w1_process() holds the mutex of the master while it
>   searches the bus and detaches the slaves which have gone:
> 
>     w1_process()                        read() of .../rw
>       mutex_lock(&dev->mutex)             kernfs active reference
>       w1_search_process()                 rw_read()
>         w1_slave_detach()                   mutex_lock(&master->mutex)
>           w1_unref_slave()                    waits
>             device_unregister()
>               waits for the reference
> 
>   The file is readable for everybody.
> 
> - The accesses through this file are not serialised with those of the
>   slave drivers, which take bus_mutex, so that two transactions can get
>   mixed up on the wire.
> 
> Take bus_mutex here as well.  It also excludes the search, which takes it
> for every pass.
> 
> Fixes: b02f8bede217 ("W1: split master mutex to avoid deadlocks.")
> Cc: stable <stable@xxxxxxxxxx>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxxxxx>

Best regards,
Krzysztof