spi: pl022: Fix race in giveback() leading to driver lock-up

commit cd6fa8d2ca53cac3226fdcffcf763be390abae32 upstream.

Commit fd316941c ("spi/pl022: disable port when unused") introduced a race,
which leads to possible driver lock up (easily reproducible on SMP).

The problem happens in giveback() function where the completion of the transfer
is signalled to SPI subsystem and then the HW SPI controller is disabled. Another
transfer might be setup in between, which brings driver in locked-up state.

Exact event sequence on SMP:

core0                                   core1

                                        => pump_transfers()
                                        /* message->state == STATE_DONE */
                                          => giveback()
                                            => spi_finalize_current_message()

=> pl022_unprepare_transfer_hardware()
=> pl022_transfer_one_message
  => flush()
  => do_interrupt_dma_transfer()
    => set_up_next_transfer()
    /* Enable SSP, turn on interrupts */
    writew((readw(SSP_CR1(pl022->virtbase)) |
           SSP_CR1_MASK_SSE), SSP_CR1(pl022->virtbase));

...

=> pl022_interrupt_handler()
  => readwriter()

                                        /* disable the SPI/SSP operation */
                                        => writew((readw(SSP_CR1(pl022->virtbase)) &
                                                  (~SSP_CR1_MASK_SSE)), SSP_CR1(pl022->virtbase));

Lockup! SPI controller is disabled and the data will never be received. Whole
SPI subsystem is waiting for transfer ACK and blocked.

So, only signal transfer completion after disabling the controller.

Fixes: fd316941c (spi/pl022: disable port when unused)
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/drivers/spi/spi-pl022.c b/drivers/spi/spi-pl022.c
index b1a9ba893fabc3cba13261c4e5b2c5096ab655fb..0bc4e4508e6f4f089472dfe1735ec964210161c8 100644 (file)
--- a/drivers/spi/spi-pl022.c
+++ b/drivers/spi/spi-pl022.c
@@ -503,12 +503,12 @@ static void giveback(struct pl022 *pl022)
        pl022->cur_msg = NULL;
        pl022->cur_transfer = NULL;
        pl022->cur_chip = NULL;
-       spi_finalize_current_message(pl022->master);
 
        /* disable the SPI/SSP operation */
        writew((readw(SSP_CR1(pl022->virtbase)) &
                (~SSP_CR1_MASK_SSE)), SSP_CR1(pl022->virtbase));
 
+       spi_finalize_current_message(pl022->master);
 }
 
 /**