mm: allow multiple error returns in try_grab_page()

In order to add checks for P2PDMA memory into try_grab_page(), expand
the error return from a bool to an int/error code. Update all the
callsites handle change in usage.

Also remove the WARN_ON_ONCE() call at the callsites seeing there
already is a WARN_ON_ONCE() inside the function if it fails.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221021174116.7200-2-logang@deltatee.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 14 insertions, 12 deletions

diff --git a/mm/gup.c b/mm/gup.c
index fe195d47de74..e2f447446384 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -202,17 +202,19 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
  * time. Cases: please see the try_grab_folio() documentation, with
  * "refs=1".
  *
- * Return: true for success, or if no action was required (if neither FOLL_PIN
- * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or
- * FOLL_PIN was set, but the page could not be grabbed.
+ * Return: 0 for success, or if no action was required (if neither FOLL_PIN
+ * nor FOLL_GET was set, nothing is done). A negative error code for failure:
+ *
+ *   -ENOMEM		FOLL_GET or FOLL_PIN was set, but the page could not
+ *			be grabbed.
  */
-bool __must_check try_grab_page(struct page *page, unsigned int flags)
+int __must_check try_grab_page(struct page *page, unsigned int flags)
 {
 	struct folio *folio = page_folio(page);
 
 	WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN));
 	if (WARN_ON_ONCE(folio_ref_count(folio) <= 0))
-		return false;
+		return -ENOMEM;
 
 	if (flags & FOLL_GET)
 		folio_ref_inc(folio);
@@ -232,7 +234,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
 		node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1);
 	}
 
-	return true;
+	return 0;
 }
 
 /**
@@ -624,8 +626,9 @@ retry:
 		       !PageAnonExclusive(page), page);
 
 	/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
-	if (unlikely(!try_grab_page(page, flags))) {
-		page = ERR_PTR(-ENOMEM);
+	ret = try_grab_page(page, flags);
+	if (unlikely(ret)) {
+		page = ERR_PTR(ret);
 		goto out;
 	}
 	/*
@@ -960,10 +963,9 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
 			goto unmap;
 		*page = pte_page(*pte);
 	}
-	if (unlikely(!try_grab_page(*page, gup_flags))) {
-		ret = -ENOMEM;
+	ret = try_grab_page(*page, gup_flags);
+	if (unlikely(ret))
 		goto unmap;
-	}
 out:
 	ret = 0;
 unmap:
@@ -2536,7 +2538,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 		}
 		SetPageReferenced(page);
 		pages[*nr] = page;
-		if (unlikely(!try_grab_page(page, flags))) {
+		if (unlikely(try_grab_page(page, flags))) {
 			undo_dev_pagemap(nr, nr_start, flags, pages);
 			break;
 		}