Commit aaa52e34 authored Nov 30, 2018 by Hugh Dickins Committed by Linus Torvalds Nov 30, 2018

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: 800d8c63 ("shmem: add huge pages support")
Fixes: f3f0e1d2 ("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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 701270fa

mm/khugepaged.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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,

mm/shmem.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -297,12 +297,14 @@ bool shmem_charge(struct inode *inode, long pages)
		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, long pages)
		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;

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