Re: [PATCH] gpu/drm/ttm: Pass GFP flags in order to avoid deadlock.

[Konrad Rzeszutek Wilk]

On Tue, May 20, 2014 at 01:40:40AM +0100, Dave Airlie wrote:
> 
> cc'ing dri-devel.

It looks pretty simple and correct . I can test it tomorrow and make sure it works
right.
> 
> > >From d0d57745ba23faf605b0f249b57d283fe1a8ee60 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Date: Mon, 19 May 2014 17:59:03 +0900
> > Subject: [PATCH] gpu/drm/ttm: Pass GFP flags in order to avoid deadlock.
> > 
> > Commit 7dc19d5a "drivers: convert shrinkers to new count/scan API" added
> > deadlock warnings that ttm_page_pool_free() and ttm_dma_page_pool_free()
> > are currently doing GFP_KERNEL allocation.
> > 
> > But these functions did not get updated to receive gfp_t argument.
> > This patch explicitly passes sc->gfp_mask or GFP_KERNEL to these functions,
> > and removes the deadlock warning.
> > 
> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/ttm/ttm_page_alloc.c     | 19 ++++++++++---------
> >  drivers/gpu/drm/ttm/ttm_page_alloc_dma.c | 19 +++++++++----------
> >  2 files changed, 19 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c b/drivers/gpu/drm/ttm/ttm_page_alloc.c
> > index 863bef9..ba8f78e 100644
> > --- a/drivers/gpu/drm/ttm/ttm_page_alloc.c
> > +++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c
> > @@ -297,8 +297,10 @@ static void ttm_pool_update_free_locked(struct ttm_page_pool *pool,
> >   *
> >   * @pool: to free the pages from
> >   * @free_all: If set to true will free all pages in pool
> > + * @gfp: GFP flags.
> >   **/
> > -static int ttm_page_pool_free(struct ttm_page_pool *pool, unsigned nr_free)
> > +static int ttm_page_pool_free(struct ttm_page_pool *pool, unsigned nr_free,
> > +			      gfp_t gfp)
> >  {
> >  	unsigned long irq_flags;
> >  	struct page *p;
> > @@ -309,8 +311,7 @@ static int ttm_page_pool_free(struct ttm_page_pool *pool, unsigned nr_free)
> >  	if (NUM_PAGES_TO_ALLOC < nr_free)
> >  		npages_to_free = NUM_PAGES_TO_ALLOC;
> >  
> > -	pages_to_free = kmalloc(npages_to_free * sizeof(struct page *),
> > -			GFP_KERNEL);
> > +	pages_to_free = kmalloc(npages_to_free * sizeof(struct page *), gfp);
> >  	if (!pages_to_free) {
> >  		pr_err("Failed to allocate memory for pool free operation\n");
> >  		return 0;
> > @@ -382,9 +383,7 @@ out:
> >   *
> >   * XXX: (dchinner) Deadlock warning!
> >   *
> > - * ttm_page_pool_free() does memory allocation using GFP_KERNEL.  that means
> > - * this can deadlock when called a sc->gfp_mask that is not equal to
> > - * GFP_KERNEL.
> > + * We need to pass sc->gfp_mask to ttm_page_pool_free().
> >   *
> >   * This code is crying out for a shrinker per pool....
> >   */
> > @@ -405,7 +404,8 @@ ttm_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> >  		if (shrink_pages == 0)
> >  			break;
> >  		pool = &_manager->pools[(i + pool_offset)%NUM_POOLS];
> > -		shrink_pages = ttm_page_pool_free(pool, nr_free);
> > +		shrink_pages = ttm_page_pool_free(pool, nr_free,
> > +						  sc->gfp_mask);
> >  		freed += nr_free - shrink_pages;
> >  	}
> >  	return freed;
> > @@ -706,7 +706,7 @@ static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
> >  	}
> >  	spin_unlock_irqrestore(&pool->lock, irq_flags);
> >  	if (npages)
> > -		ttm_page_pool_free(pool, npages);
> > +		ttm_page_pool_free(pool, npages, GFP_KERNEL);
> >  }
> >  
> >  /*
> > @@ -846,7 +846,8 @@ void ttm_page_alloc_fini(void)
> >  	ttm_pool_mm_shrink_fini(_manager);
> >  
> >  	for (i = 0; i < NUM_POOLS; ++i)
> > -		ttm_page_pool_free(&_manager->pools[i], FREE_ALL_PAGES);
> > +		ttm_page_pool_free(&_manager->pools[i], FREE_ALL_PAGES,
> > +				   GFP_KERNEL);
> >  
> >  	kobject_put(&_manager->kobj);
> >  	_manager = NULL;
> > diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> > index fb8259f..1b79bf0 100644
> > --- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> > +++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> > @@ -411,8 +411,10 @@ static void ttm_dma_page_put(struct dma_pool *pool, struct dma_page *d_page)
> >   *
> >   * @pool: to free the pages from
> >   * @nr_free: If set to true will free all pages in pool
> > + * @gfp: GFP flags.
> >   **/
> > -static unsigned ttm_dma_page_pool_free(struct dma_pool *pool, unsigned nr_free)
> > +static unsigned ttm_dma_page_pool_free(struct dma_pool *pool, unsigned nr_free,
> > +				       gfp_t gfp)
> >  {
> >  	unsigned long irq_flags;
> >  	struct dma_page *dma_p, *tmp;
> > @@ -430,8 +432,7 @@ static unsigned ttm_dma_page_pool_free(struct dma_pool *pool, unsigned nr_free)
> >  			 npages_to_free, nr_free);
> >  	}
> >  #endif
> > -	pages_to_free = kmalloc(npages_to_free * sizeof(struct page *),
> > -			GFP_KERNEL);
> > +	pages_to_free = kmalloc(npages_to_free * sizeof(struct page *), gfp);
> >  
> >  	if (!pages_to_free) {
> >  		pr_err("%s: Failed to allocate memory for pool free operation\n",
> > @@ -530,7 +531,7 @@ static void ttm_dma_free_pool(struct device *dev, enum pool_type type)
> >  		if (pool->type != type)
> >  			continue;
> >  		/* Takes a spinlock.. */
> > -		ttm_dma_page_pool_free(pool, FREE_ALL_PAGES);
> > +		ttm_dma_page_pool_free(pool, FREE_ALL_PAGES, GFP_KERNEL);
> >  		WARN_ON(((pool->npages_in_use + pool->npages_free) != 0));
> >  		/* This code path is called after _all_ references to the
> >  		 * struct device has been dropped - so nobody should be
> > @@ -983,7 +984,7 @@ void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
> >  
> >  	/* shrink pool if necessary (only on !is_cached pools)*/
> >  	if (npages)
> > -		ttm_dma_page_pool_free(pool, npages);
> > +		ttm_dma_page_pool_free(pool, npages, GFP_KERNEL);
> >  	ttm->state = tt_unpopulated;
> >  }
> >  EXPORT_SYMBOL_GPL(ttm_dma_unpopulate);
> > @@ -993,10 +994,7 @@ EXPORT_SYMBOL_GPL(ttm_dma_unpopulate);
> >   *
> >   * XXX: (dchinner) Deadlock warning!
> >   *
> > - * ttm_dma_page_pool_free() does GFP_KERNEL memory allocation, and so attention
> > - * needs to be paid to sc->gfp_mask to determine if this can be done or not.
> > - * GFP_KERNEL memory allocation in a GFP_ATOMIC reclaim context woul dbe really
> > - * bad.
> > + * We need to pass sc->gfp_mask to ttm_dma_page_pool_free().
> >   *
> >   * I'm getting sadder as I hear more pathetical whimpers about needing per-pool
> >   * shrinkers
> > @@ -1027,7 +1025,8 @@ ttm_dma_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> >  		if (++idx < pool_offset)
> >  			continue;
> >  		nr_free = shrink_pages;
> > -		shrink_pages = ttm_dma_page_pool_free(p->pool, nr_free);
> > +		shrink_pages = ttm_dma_page_pool_free(p->pool, nr_free,
> > +						      sc->gfp_mask);
> >  		freed += nr_free - shrink_pages;
> >  
> >  		pr_debug("%s: (%s:%d) Asked to shrink %d, have %d more to go\n",
> > 
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