On Thu, 18 Nov 2021, Matthew Wilcox wrote:

On Wed, Nov 17, 2021 at 03:39:30PM +1100, NeilBrown wrote:

quoted

+++ b/drivers/iommu/tegra-smmu.c

@@ -676,12 +676,12 @@ static struct page *as_get_pde_page(struct tegra_smmu_as *as,
 	 * allocate page in a sleeping context if GFP flags permit. Hence
 	 * spinlock needs to be unlocked and re-locked after allocation.
 	 */
-	if (!(gfp & __GFP_ATOMIC))
+	if (gfp & __GFP_DIRECT_RECLAIM)
 		spin_unlock_irqrestore(&as->lock, *flags);
 
 	page = alloc_page(gfp | __GFP_DMA | __GFP_ZERO);
 
-	if (!(gfp & __GFP_ATOMIC))
+	if (gfp & __GFP_DIRECT_RECLAIM)
 		spin_lock_irqsave(&as->lock, *flags);
 
 	/*

Surely this should be gfpflags_allow_blocking() instead of poking about
in the innards of gfp flags?

Possibly.  Didn't know about gfpflags_allow_blocking().  From a quick
grep in the kernel, a whole lot of other people don't know about it
either, though clearly some do.

Maybe we should reaname "__GFP_DIRECT_RECLAIM" to
"__GFP_ALLOW_BLOCKING", because that is what most users seems to care
about.

If not, then we probably want a gfpflags_without_block() function that
removes that flag, as lots of code wants to do that - and using the flag
for one, and an inline for the other is not consistent.

My leaning would be to __GFP_ALLOW_BLOCKING

NeilBrown

This patch seems like a good simplification to me.

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Thanks,
NeilBrown