drm/i915: Protect WC stash allocation against direct reclaim

Web:        https://git.kernel.org/torvalds/c/124804c4c4b2e84e956cedd17878562e230a907f
Commit:     124804c4c4b2e84e956cedd17878562e230a907f
Parent:     c5bd1fc9a6c843c85a5cea5765cdc997f832df3c
Refname:    refs/heads/master
Author:     Chris Wilson <[email protected]>
AuthorDate: Sun Jan 21 17:31:43 2018 +0000
Committer:  Rodrigo Vivi <[email protected]>
CommitDate: Thu Feb 1 07:32:46 2018 -0800

    drm/i915: Protect WC stash allocation against direct reclaim
    
    As we attempt to allocate pages for use in a new WC stash, direct
    reclaim may run underneath us and fill up the WC stash. We have to be
    careful then not to overflow the pvec.
    
    Fixes: 66df1014efba ("drm/i915: Keep a small stash of preallocated WC pages")
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103109
    Signed-off-by: Chris Wilson <[email protected]>
    Cc: Matthew Auld <[email protected]>
    Cc: Joonas Lahtinen <[email protected]>
    Reviewed-by: Matthew Auld <[email protected]>
    Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
    (cherry picked from commit 073cd7816685ac77c6d8b4d321a5586c9177b76a)
    Signed-off-by: Rodrigo Vivi <[email protected]>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 0de4f3f13fc4..133cb9590003 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -377,6 +377,7 @@ static gen6_pte_t iris_pte_encode(dma_addr_t addr,
 static struct page *vm_alloc_page(struct i915_address_space *vm, gfp_t gfp)
 {
 	struct pagevec *pvec = &vm->free_pages;
+	struct pagevec stash;
 
 	if (I915_SELFTEST_ONLY(should_fail(&vm->fault_attr, 1)))
 		i915_gem_shrink_all(vm->i915);
@@ -395,7 +396,15 @@ static struct page *vm_alloc_page(struct i915_address_space *vm, gfp_t gfp)
 	if (likely(pvec->nr))
 		return pvec->pages[--pvec->nr];
 
-	/* Otherwise batch allocate pages to amoritize cost of set_pages_wc. */
+	/*
+	 * Otherwise batch allocate pages to amoritize cost of set_pages_wc.
+	 *
+	 * We have to be careful as page allocation may trigger the shrinker
+	 * (via direct reclaim) which will fill up the WC stash underneath us.
+	 * So we add our WB pages into a temporary pvec on the stack and merge
+	 * them into the WC stash after all the allocations are complete.
+	 */
+	pagevec_init(&stash);
 	do {
 		struct page *page;
 
@@ -403,15 +412,24 @@ static struct page *vm_alloc_page(struct i915_address_space *vm, gfp_t gfp)
 		if (unlikely(!page))
 			break;
 
-		pvec->pages[pvec->nr++] = page;
-	} while (pagevec_space(pvec));
+		stash.pages[stash.nr++] = page;
+	} while (stash.nr < pagevec_space(pvec));
 
-	if (unlikely(!pvec->nr))
-		return NULL;
+	if (stash.nr) {
+		int nr = min_t(int, stash.nr, pagevec_space(pvec));
+		struct page **pages = stash.pages + stash.nr - nr;
 
-	set_pages_array_wc(pvec->pages, pvec->nr);
+		if (nr && !set_pages_array_wc(pages, nr)) {
+			memcpy(pvec->pages + pvec->nr,
+			       pages, sizeof(pages[0]) * nr);
+			pvec->nr += nr;
+			stash.nr -= nr;
+		}
+
+		pagevec_release(&stash);
+	}
 
-	return pvec->pages[--pvec->nr];
+	return likely(pvec->nr) ? pvec->pages[--pvec->nr] : NULL;
 }
 
 static void vm_free_pages_release(struct i915_address_space *vm,
--
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