On Friday, April 13, 2018 1:35:45 PM PDT Kenneth Graunke wrote: > On Monday, April 9, 2018 4:06:16 PM PDT James Xiong wrote: > > From: "Xiong, James" <james.xi...@intel.com> > > > > On non-LLC platforms, we malloc shadow batch/state buffers > > of the same sizes as our batch/state buffers' GEM allocations. > > However the buffer allocator reuses similar-sized gem objects, > > it returns a buffer larger than we asked for in some cases > > and we end up with smaller shadow buffers. If we utilize the > > full-size of the over-allocated batch/state buffers, we may wind > > up accessing beyond the bounds of the shadow buffers and cause > > segmentation fault and/or memory corruption. > > Oh, good catch! We do indeed malloc too little if the bufmgr rounds up > the BO size. Thanks for finding this! > > > A few examples: > > case batch state > > request bo shadow request bo shadow > > init 0 20K 20K 20K 16K 16K 16K > > grow_buffer 1 30K 32K 30K 24K 24K 24K > > grow_buffer 2 48K 48K 48K 36K 40K 36K > > grow_buffer 3 72K 80K 72K 60K 64K 60K > > grow_buffer 4 120K 128K 120K - - - > > > > batch #1, #3, #4; state #2 and #3 are problematic. We can change > > the order to allocate the bo first, then allocate the shadow > > buffer using the bo's size so that the shadow buffer have at > > least an equivalent size of the gem allocation. > > > > Another problem: even though the state/batch buffer could grow, > > when checking if it runs out space, we always compare with the > > initial batch/state sizes. To utilize the entire buffers, change > > to compare with the actual sizes. > > This is actually intentional. Our goal is to flush batches when the > amount of commands or state reaches those thresholds. Occasionally, > we'll be in the middle of emitting a draw, and unable to stop. In that > case, we grow the batch and keep going. But after that, we're beyond > our original target, so we flush next time. We don't want to grow > without bounds...it's meant more for emergencies, or if we've badly > estimated the size of the draw call. > > I've sent a simpler patch which I think should hopefully fix your bug: > https://patchwork.freedesktop.org/patch/217107/
Lionel noticed that I botched that patch. Here's an actual one: https://patchwork.freedesktop.org/patch/217108/
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