Messages in this thread | | | Subject | Re: [PATCH] spi: Fix incomplete handling of SPI_MASTER_MUST_RX/_MUST_TX | From | Purna Chandra Mandal <> | Date | Tue, 1 Mar 2016 17:47:49 +0530 |
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Mark,
On 02/08/2016 09:45 PM, Mark Brown wrote:
> On Fri, Feb 05, 2016 at 10:30:24AM +0530, Purna Chandra Mandal wrote: > > Please fix your mail client to word wrap within paragraphs at something > substantially less than 80 columns. Doing this makes your messages much > easier to read and reply to. > >> Idea is good, but not sufficient. >> Dummy buffers are _reallocated_ to accommodate larger size of transfer. In this if >> [originally NULL] .rx_buf/.tx_buf is not reset back to NULL after the transfer >> is over spi-core will find those .rx/tx_buf non-NULL in next _transfer() call and >> will pass the stale rx/tx_buf to spi controller driver which will definitely >> corrupt the memory and crash the system. > This needs to be clear to readers; a fairly obvious way of dealing with > this would be to rellocate down to a page rather than freeing.
Yea. But current krealloc() implementation allocates new memory if new size is more than the allocated space, (and frees the old). If we allocate PAGE_SIZE of dummy buffer (at first call irrespective of required size), re-use it and don't allow transfer size to grow more than PAGE_SIZE we will be fine provided all SPI clients agree to the size restriction. The moment we'll try to re-allocate new buffer we will reach the same point we wanted to avoid here.
>> Above all the whole design depends on trust that core will not play with any data-structure >> which will break object-oriented/layered approach. So better to undo the modification >> (when needed to facilitate some functionality) unless core wants those information to be passed >> back to caller/client for reporting success or error or else. > That's really not the case, we already make a range of other > modifications to complete partially filled transfers in order to > simplify driver code.
Purna
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