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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: 800d8c63b2 ("shmem: add huge pages support")
Fixes: f3f0e1d215 ("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>
This commit is contained in:
Hugh Dickins 2018-11-30 14:10:29 -08:00 committed by Linus Torvalds
parent 701270fa19
commit aaa52e3400
2 changed files with 9 additions and 2 deletions
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5
mm/khugepaged.c
View File

@ -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,

6
mm/shmem.c
View File

@ -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;