On Tue, Nov 26, 2013 at 04:55:50PM -0800, Ben Widawsky wrote:
> If we end up calling the shrinker, which in turn requires the OOM
> killer, we may end up infinitely waiting for a process to die if the OOM
> chooses. The case that this prevents occurs in execbuf. The forked
> variants of gem_evict_everything is a good way to hit it. This is
> exacerbated by Daniel's recent patch to give OOM precedence to the GEM
> tests.
>
> It's a twisted form of a deadlock.
>
> What occurs is the following (assume just 2 procs)
> 1. proc A gets to execbuf while out of memory, gets struct_mutex.
> 2. OOM killer comes in and chooses proc B
> 3. proc B closes it's fds, which requires struct mutex, blocks
> 4, OOM killer waits for B to die before killing another process (this
> part is speculative)
>
It appears that by itself, this patch is insufficient to prevent the
failure when run in piglit. Before I go on a wild goose chase of finding
all allocations, maybe I'll give people a chance to chime in. The
symptom is the same always, OOM, procs can't die because struct_mutex is
held.
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Ben Widawsky <ben@xxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index fb2d548..a60894d 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1842,12 +1842,12 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> BUG_ON(obj->base.read_domains & I915_GEM_GPU_DOMAINS);
> BUG_ON(obj->base.write_domain & I915_GEM_GPU_DOMAINS);
>
> - st = kmalloc(sizeof(*st), GFP_KERNEL);
> + st = kmalloc(sizeof(*st), GFP_NOWAIT);
> if (st == NULL)
> return -ENOMEM;
>
> page_count = obj->base.size / PAGE_SIZE;
> - if (sg_alloc_table(st, page_count, GFP_KERNEL)) {
> + if (sg_alloc_table(st, page_count, GFP_NOWAIT)) {
> kfree(st);
> return -ENOMEM;
> }
> --
> 1.8.4.2
>
--
Ben Widawsky, Intel Open Source Technology Center
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