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From:   john.hubbard@gmail.com
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
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        David Airlie <airlied@linux.ie>,
        "David S . Miller" <davem@davemloft.net>,
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        Jason Gunthorpe <jgg@ziepe.ca>, Jens Axboe <axboe@kernel.dk>,
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        Johannes Thumshirn <jthumshirn@suse.de>,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Ming Lei <ming.lei@redhat.com>, Sage Weil <sage@redhat.com>,
        Santosh Shilimkar <santosh.shilimkar@oracle.com>,
        Yan Zheng <zyan@redhat.com>, netdev@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-mm@kvack.org,
        linux-rdma@vger.kernel.org, bpf@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Ira Weiny <ira.weiny@intel.com>
Subject: [PATCH v3 1/3] mm/gup: add make_dirty arg to put_user_pages_dirty_lock()
Date:   Tue, 23 Jul 2019 21:45:35 -0700
Message-Id: <20190724044537.10458-2-jhubbard@nvidia.com>
In-Reply-To: <20190724044537.10458-1-jhubbard@nvidia.com>
References: <20190724044537.10458-1-jhubbard@nvidia.com>
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From: John Hubbard <jhubbard@nvidia.com>

Provide more capable variation of put_user_pages_dirty_lock(),
and delete put_user_pages_dirty(). This is based on the
following:

1. Lots of call sites become simpler if a bool is passed
into put_user_page*(), instead of making the call site
choose which put_user_page*() variant to call.

2. Christoph Hellwig's observation that set_page_dirty_lock()
is usually correct, and set_page_dirty() is usually a
bug, or at least questionable, within a put_user_page*()
calling chain.

This leads to the following API choices:

    * put_user_pages_dirty_lock(page, npages, make_dirty)

    * There is no put_user_pages_dirty(). You have to
      hand code that, in the rare case that it's
      required.

Cc: Matthew Wilcox <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/infiniband/core/umem.c             |   5 +-
 drivers/infiniband/hw/hfi1/user_pages.c    |   5 +-
 drivers/infiniband/hw/qib/qib_user_pages.c |   5 +-
 drivers/infiniband/hw/usnic/usnic_uiom.c   |   5 +-
 drivers/infiniband/sw/siw/siw_mem.c        |   8 +-
 include/linux/mm.h                         |   5 +-
 mm/gup.c                                   | 115 +++++++++------------
 7 files changed, 58 insertions(+), 90 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 08da840ed7ee..965cf9dea71a 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -54,10 +54,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
 
 	for_each_sg_page(umem->sg_head.sgl, &sg_iter, umem->sg_nents, 0) {
 		page = sg_page_iter_page(&sg_iter);
-		if (umem->writable && dirty)
-			put_user_pages_dirty_lock(&page, 1);
-		else
-			put_user_page(page);
+		put_user_pages_dirty_lock(&page, 1, umem->writable && dirty);
 	}
 
 	sg_free_table(&umem->sg_head);
diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c
index b89a9b9aef7a..469acb961fbd 100644
--- a/drivers/infiniband/hw/hfi1/user_pages.c
+++ b/drivers/infiniband/hw/hfi1/user_pages.c
@@ -118,10 +118,7 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np
 void hfi1_release_user_pages(struct mm_struct *mm, struct page **p,
 			     size_t npages, bool dirty)
 {
-	if (dirty)
-		put_user_pages_dirty_lock(p, npages);
-	else
-		put_user_pages(p, npages);
+	put_user_pages_dirty_lock(p, npages, dirty);
 
 	if (mm) { /* during close after signal, mm can be NULL */
 		atomic64_sub(npages, &mm->pinned_vm);
diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c
index bfbfbb7e0ff4..6bf764e41891 100644
--- a/drivers/infiniband/hw/qib/qib_user_pages.c
+++ b/drivers/infiniband/hw/qib/qib_user_pages.c
@@ -40,10 +40,7 @@
 static void __qib_release_user_pages(struct page **p, size_t num_pages,
 				     int dirty)
 {
-	if (dirty)
-		put_user_pages_dirty_lock(p, num_pages);
-	else
-		put_user_pages(p, num_pages);
+	put_user_pages_dirty_lock(p, num_pages, dirty);
 }
 
 /**
diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c
index 0b0237d41613..62e6ffa9ad78 100644
--- a/drivers/infiniband/hw/usnic/usnic_uiom.c
+++ b/drivers/infiniband/hw/usnic/usnic_uiom.c
@@ -75,10 +75,7 @@ static void usnic_uiom_put_pages(struct list_head *chunk_list, int dirty)
 		for_each_sg(chunk->page_list, sg, chunk->nents, i) {
 			page = sg_page(sg);
 			pa = sg_phys(sg);
-			if (dirty)
-				put_user_pages_dirty_lock(&page, 1);
-			else
-				put_user_page(page);
+			put_user_pages_dirty_lock(&page, 1, dirty);
 			usnic_dbg("pa: %pa\n", &pa);
 		}
 		kfree(chunk);
diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
index 67171c82b0c4..358d440efa11 100644
--- a/drivers/infiniband/sw/siw/siw_mem.c
+++ b/drivers/infiniband/sw/siw/siw_mem.c
@@ -65,13 +65,7 @@ static void siw_free_plist(struct siw_page_chunk *chunk, int num_pages,
 {
 	struct page **p = chunk->plist;
 
-	while (num_pages--) {
-		if (!PageDirty(*p) && dirty)
-			put_user_pages_dirty_lock(p, 1);
-		else
-			put_user_page(*p);
-		p++;
-	}
+	put_user_pages_dirty_lock(chunk->plist, num_pages, dirty);
 }
 
 void siw_umem_release(struct siw_umem *umem, bool dirty)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0334ca97c584..9759b6a24420 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1057,8 +1057,9 @@ static inline void put_user_page(struct page *page)
 	put_page(page);
 }
 
-void put_user_pages_dirty(struct page **pages, unsigned long npages);
-void put_user_pages_dirty_lock(struct page **pages, unsigned long npages);
+void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
+			       bool make_dirty);
+
 void put_user_pages(struct page **pages, unsigned long npages);
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/mm/gup.c b/mm/gup.c
index 98f13ab37bac..7fefd7ab02c4 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -29,85 +29,70 @@ struct follow_page_context {
 	unsigned int page_mask;
 };
 
-typedef int (*set_dirty_func_t)(struct page *page);
-
-static void __put_user_pages_dirty(struct page **pages,
-				   unsigned long npages,
-				   set_dirty_func_t sdf)
-{
-	unsigned long index;
-
-	for (index = 0; index < npages; index++) {
-		struct page *page = compound_head(pages[index]);
-
-		/*
-		 * Checking PageDirty at this point may race with
-		 * clear_page_dirty_for_io(), but that's OK. Two key cases:
-		 *
-		 * 1) This code sees the page as already dirty, so it skips
-		 * the call to sdf(). That could happen because
-		 * clear_page_dirty_for_io() called page_mkclean(),
-		 * followed by set_page_dirty(). However, now the page is
-		 * going to get written back, which meets the original
-		 * intention of setting it dirty, so all is well:
-		 * clear_page_dirty_for_io() goes on to call
-		 * TestClearPageDirty(), and write the page back.
-		 *
-		 * 2) This code sees the page as clean, so it calls sdf().
-		 * The page stays dirty, despite being written back, so it
-		 * gets written back again in the next writeback cycle.
-		 * This is harmless.
-		 */
-		if (!PageDirty(page))
-			sdf(page);
-
-		put_user_page(page);
-	}
-}
-
 /**
- * put_user_pages_dirty() - release and dirty an array of gup-pinned pages
- * @pages:  array of pages to be marked dirty and released.
+ * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
+ * @pages:  array of pages to be maybe marked dirty, and definitely released.
  * @npages: number of pages in the @pages array.
+ * @make_dirty: whether to mark the pages dirty
  *
  * "gup-pinned page" refers to a page that has had one of the get_user_pages()
  * variants called on that page.
  *
  * For each page in the @pages array, make that page (or its head page, if a
- * compound page) dirty, if it was previously listed as clean. Then, release
- * the page using put_user_page().
+ * compound page) dirty, if @make_dirty is true, and if the page was previously
+ * listed as clean. In any case, releases all pages using put_user_page(),
+ * possibly via put_user_pages(), for the non-dirty case.
  *
  * Please see the put_user_page() documentation for details.
  *
- * set_page_dirty(), which does not lock the page, is used here.
- * Therefore, it is the caller's responsibility to ensure that this is
- * safe. If not, then put_user_pages_dirty_lock() should be called instead.
+ * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
+ * required, then the caller should a) verify that this is really correct,
+ * because _lock() is usually required, and b) hand code it:
+ * set_page_dirty_lock(), put_user_page().
  *
  */
-void put_user_pages_dirty(struct page **pages, unsigned long npages)
+void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
+			       bool make_dirty)
 {
-	__put_user_pages_dirty(pages, npages, set_page_dirty);
-}
-EXPORT_SYMBOL(put_user_pages_dirty);
+	unsigned long index;
 
-/**
- * put_user_pages_dirty_lock() - release and dirty an array of gup-pinned pages
- * @pages:  array of pages to be marked dirty and released.
- * @npages: number of pages in the @pages array.
- *
- * For each page in the @pages array, make that page (or its head page, if a
- * compound page) dirty, if it was previously listed as clean. Then, release
- * the page using put_user_page().
- *
- * Please see the put_user_page() documentation for details.
- *
- * This is just like put_user_pages_dirty(), except that it invokes
- * set_page_dirty_lock(), instead of set_page_dirty().
- *
- */
-void put_user_pages_dirty_lock(struct page **pages, unsigned long npages)
-{
-	__put_user_pages_dirty(pages, npages, set_page_dirty_lock);
+	/*
+	 * TODO: this can be optimized for huge pages: if a series of pages is
+	 * physically contiguous and part of the same compound page, then a
+	 * single operation to the head page should suffice.
+	 */
+
+	if (!make_dirty) {
+		put_user_pages(pages, npages);
+		return;
+	}
+
+	for (index = 0; index < npages; index++) {
+		struct page *page = compound_head(pages[index]);
+		/*
+		 * Checking PageDirty at this point may race with
+		 * clear_page_dirty_for_io(), but that's OK. Two key
+		 * cases:
+		 *
+		 * 1) This code sees the page as already dirty, so it
+		 * skips the call to set_page_dirty(). That could happen
+		 * because clear_page_dirty_for_io() called
+		 * page_mkclean(), followed by set_page_dirty().
+		 * However, now the page is going to get written back,
+		 * which meets the original intention of setting it
+		 * dirty, so all is well: clear_page_dirty_for_io() goes
+		 * on to call TestClearPageDirty(), and write the page
+		 * back.
+		 *
+		 * 2) This code sees the page as clean, so it calls
+		 * set_page_dirty(). The page stays dirty, despite being
+		 * written back, so it gets written back again in the
+		 * next writeback cycle. This is harmless.
+		 */
+		if (!PageDirty(page))
+			set_page_dirty_lock(page);
+		put_user_page(page);
+	}
 }
 EXPORT_SYMBOL(put_user_pages_dirty_lock);
 
-- 
2.22.0