Re: [PATCH] spi: Fix deadlock when adding SPI controllers on SPI buses

[Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>]

On Thu, Oct 24, 2024 at 08:26:11PM +0530, Hardik Gohil wrote:
> From: Mark Brown <broonie@xxxxxxxxxx>
> 
> [ Upstream commit 6098475d4cb48d821bdf453c61118c56e26294f0 ]
> 
> Currently we have a global spi_add_lock which we take when adding new
> devices so that we can check that we're not trying to reuse a chip
> select that's already controlled.  This means that if the SPI device is
> itself a SPI controller and triggers the instantiation of further SPI
> devices we trigger a deadlock as we try to register and instantiate
> those devices while in the process of doing so for the parent controller
> and hence already holding the global spi_add_lock.  Since we only care
> about concurrency within a single SPI bus move the lock to be per
> controller, avoiding the deadlock.
> 
> This can be easily triggered in the case of spi-mux.
> 
> Reported-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> Signed-off-by: Hardik Gohil <hgohil@xxxxxxxxxx>
> ---
> This fix was not backported to v5.4 and 5.10
> 
> Along with this fix please also apply this fix on top of this
> 
> spi: fix use-after-free of the add_lock mutex
> commit 6c53b45c71b4920b5e62f0ea8079a1da382b9434 upstream.
> 
> Commit 6098475d4cb4 ("spi: Fix deadlock when adding SPI controllers on
> SPI buses") introduced a per-controller mutex. But mutex_unlock() of
> said lock is called after the controller is already freed:

Now both queued up, thanks.

greg k-h