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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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