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SubjectRe: [spi-devel-general] [patch 2.6.15-rc5-mm2] SPI, priority inversion tweak
So you're turning this to be unsafe if the buffer is in use, right? Funny...

David Brownell wrote:

>This is an updated version of the patch from Mark Underwood, handling
>the no-memory case better and using SLAB_KERNEL not SLAB_ATOMIC.
>
>Please apply it on top of the current SPI code in the MM tree.
>
>- Dave
>
>
>------------------------------------------------------------------------
>
>Update the SPI framework to remove a potential priority inversion case by
>reverting to kmalloc if the pre-allocated DMA-safe buffer isn't available.
>
>From: Mark Underwood <basicmark@yahoo.com>
>Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
>
>--- g26.orig/drivers/spi/spi.c 2005-12-11 11:06:38.000000000 -0800
>+++ g26/drivers/spi/spi.c 2005-12-13 09:56:22.000000000 -0800
>@@ -541,22 +541,30 @@ int spi_write_then_read(struct spi_devic
> int status;
> struct spi_message message;
> struct spi_transfer x[2];
>+ u8 *local_buf;
>
> /* Use preallocated DMA-safe buffer. We can't avoid copying here,
> * (as a pure convenience thing), but we can keep heap costs
>- * out of the hot path.
>+ * out of the hot path ...
> */
> if ((n_tx + n_rx) > SPI_BUFSIZ)
> return -EINVAL;
>
>- down(&lock);
>+ /* ... unless someone else is using the pre-allocated buffer */
>+ if (down_trylock(&lock)) {
>+ local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
>+ if (!local_buf)
>+ return -ENOMEM;
>+ } else
>+ local_buf = buf;
>+
> memset(x, 0, sizeof x);
>
>- memcpy(buf, txbuf, n_tx);
>- x[0].tx_buf = buf;
>+ memcpy(local_buf, txbuf, n_tx);
>+ x[0].tx_buf = local_buf;
> x[0].len = n_tx;
>
>- x[1].rx_buf = buf + n_tx;
>+ x[1].rx_buf = local_buf + n_tx;
> x[1].len = n_rx;
>
> /* do the i/o */
>@@ -568,7 +576,11 @@ int spi_write_then_read(struct spi_devic
> status = message.status;
> }
>
>- up(&lock);
>+ if (x[0].tx_buf == buf)
>+ up(&lock);
>+ else
>+ kfree(local_buf);
>+
> return status;
> }
> EXPORT_SYMBOL_GPL(spi_write_then_read);
>
>

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