Hi Laurent, On 06/19/2012 11:00 PM, Laurent Pinchart wrote: > Hi Tomasz, > > Thanks for the patch. > > On Thursday 14 June 2012 15:37:40 Tomasz Stanislawski wrote: >> This patch removes a reference to alloc_ctx from an instance of a DMA >> contiguous buffer. It helps to avoid a risk of a dangling pointer if the >> context is released while the buffer is still valid. > > Can this really happen ? All drivers except marvell-ccic seem to call > vb2_dma_contig_cleanup_ctx() in their remove handler and probe cleanup path > only. Freeing the context while buffers are still around would be a driver > bug, and I expect drivers to destroy the queue in that case anyway. > > This being said, removing the dereference step is a good idea, so I think the > patch should be applied, possibly with a different commit message. > The problem may happen if a DMABUF sharing is used. - process A uses V4L2 queue to create a buffer - process A exports a buffer and shares it with the process B (by sockets or /proc/pid/fd) - the process A gets killed, queue is destroyed - someone call rmmod on v4l driver, alloc_ctx is freed - process B keeps reference to a buffer that has a dangling reference to alloc_ctx The presented scenario might be a bit too pathological and artificial. Moreover it involves root privileges. But it is possible to trigger this bug. One solution might be keeping reference count in alloc_ctx but it would be easier to get rid of the reference to alloc_ctx from vb2-dma-contig buffer. BTW. I decided to drop 'Remove unneeded allocation context structure' because Marek Szyprowski is working on extension to vb2-dma-contig that allow to create buffers with no kernel mappings. That feature involved additional parameter to alloc_ctx other than pointer to the device. Regards, Tomasz Stanislawski >> Moreover it removes one >> dereference step while accessing a device structure. >> >> Signed-off-by: Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx> >> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > >> + dma_free_coherent(buf->dev, buf->size, buf->vaddr, >> buf->dma_addr); >> kfree(buf); >> } _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
