+ mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch added to -mm tree

+ mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/khugepaged: fix crashes due to misaccounted holes
has been added to the -mm tree.  Its filename is
     mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch

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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm/khugepaged: fix crashes due to misaccounted holes

Huge tmpfs testing on a shortish file mapped into a pmd-rounded extent hit
shmem_evict_inode()'s WARN_ON(inode->i_blocks) followed by clear_inode()'s
BUG_ON(inode->i_data.nrpages) when the file was later closed and unlinked.

khugepaged's collapse_shmem() was forgetting to update mapping->nrpages on
the rollback path, after it had added but then needs to undo some holes.

There is indeed an irritating asymmetry between shmem_charge(), whose
callers want it to increment nrpages after successfully accounting blocks,
and shmem_uncharge(), when __delete_from_page_cache() already decremented
nrpages itself: oh well, just add a comment on that to them both.

And shmem_recalc_inode() is supposed to be called when the accounting is
expected to be in balance (so it can deduce from imbalance that reclaim
discarded some pages): so change shmem_charge() to update nrpages earlier
(though it's rare for the difference to matter at all).

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261523450.2275@eggly.anvils
Fixes: 800d8c63b2e98 ("shmem: add huge pages support")
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/khugepaged.c~mm-khugepaged-fix-crashes-due-to-misaccounted-holes
+++ a/mm/khugepaged.c
@@ -1506,9 +1506,12 @@ xa_unlocked:
 		khugepaged_pages_collapsed++;
 	} else {
 		struct page *page;
+
 		/* Something went wrong: roll back page cache changes */
-		shmem_uncharge(mapping->host, nr_none);
 		xas_lock_irq(&xas);
+		mapping->nrpages -= nr_none;
+		shmem_uncharge(mapping->host, nr_none);
+
 		xas_set(&xas, start);
 		xas_for_each(&xas, page, end - 1) {
 			page = list_first_entry_or_null(&pagelist,
--- a/mm/shmem.c~mm-khugepaged-fix-crashes-due-to-misaccounted-holes
+++ a/mm/shmem.c
@@ -297,12 +297,14 @@ bool shmem_charge(struct inode *inode, l
 	if (!shmem_inode_acct_block(inode, pages))
 		return false;
 
+	/* nrpages adjustment first, then shmem_recalc_inode() when balanced */
+	inode->i_mapping->nrpages += pages;
+
 	spin_lock_irqsave(&info->lock, flags);
 	info->alloced += pages;
 	inode->i_blocks += pages * BLOCKS_PER_PAGE;
 	shmem_recalc_inode(inode);
 	spin_unlock_irqrestore(&info->lock, flags);
-	inode->i_mapping->nrpages += pages;
 
 	return true;
 }
@@ -312,6 +314,8 @@ void shmem_uncharge(struct inode *inode,
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	unsigned long flags;
 
+	/* nrpages adjustment done by __delete_from_page_cache() or caller */
+
 	spin_lock_irqsave(&info->lock, flags);
 	info->alloced -= pages;
 	inode->i_blocks -= pages * BLOCKS_PER_PAGE;
_

Patches currently in -mm which might be from hughd@google.com are

mm-huge_memory-rename-freeze_page-to-unmap_page.patch
mm-huge_memory-splitting-set-mappingindex-before-unfreeze.patch
mm-huge_memory-fix-lockdep-complaint-on-32-bit-i_size_read.patch
mm-khugepaged-collapse_shmem-stop-if-punched-or-truncated.patch
mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch
mm-khugepaged-collapse_shmem-remember-to-clear-holes.patch
mm-khugepaged-minor-reorderings-in-collapse_shmem.patch
mm-khugepaged-collapse_shmem-without-freezing-new_page.patch
mm-khugepaged-collapse_shmem-do-not-crash-on-compound.patch
mm-khugepaged-fix-the-xas_create_range-error-path.patch
mm-put_and_wait_on_page_locked-while-page-is-migrated.patch