[U-Boot] [U-Boot,05/10] dfu: don't keep freeing/reallocating

[Tom Rini]

On Fri, Sep 04, 2015 at 10:03:46PM -0600, Stephen Warren wrote:

> From: Stephen Warren <swarren at nvidia.com>
> 
> DFU currently allocates buffer memory at the start of each data transfer
> operation and frees it at the end. Especially since memalign() is used to
> allocate the buffer, and various other allocations happen during the
> transfer, this can expose the code to heap fragmentation, which prevents
> the allocation from succeeding on subsequent transfers.
> 
> Fix the code to allocate the buffer once when DFU mode is initialized,
> and free the buffer once when DFU mode is exited, to reduce the exposure
> to heap fragmentation.
> 
> The failure mode is:
> 
> // Internally to memalign(), this allocates a lot more than s to guarantee
> // that alignment can occur, then returns chunks of memory at the start/
> // end of the allocated buffer to the heap.
> p = memalign(a, s);
> // Various other malloc()s occur here, some of which allocate the RAM
> // immediately before/after "p".
> //
> // DFU transfer is complete, so buffer is released.
> free(p);
> // By chance, no other malloc()/free() here, in DFU at least.
> //
> // A new DFU transfer starts, so the buffer is allocated again.
> // In theory this should succeed since we just free()d a buffer of the
> // same size. However, this fails because memalign() internally attempts
> // to allocate much more than "s", yet free(p) above only free()d a
> // little more than "s".
> p = memalign(a, s);
> 
> Signed-off-by: Stephen Warren <swarren at nvidia.com>
> Acked-by: Lukasz Majewski <l.majewski at samsung.com>
> Tested-by: Lukasz Majewski <l.majewski at samsung.com>

Applied to u-boot/master, thanks!

-- 
Tom
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