Commit b1cc94ab authored Sep 06, 2017 by Mike Rapoport Committed by Linus Torvalds Sep 06, 2017

shmem: shmem_charge: verify max_block is not exceeded before inode update

Patch series "userfaultfd: enable zeropage support for shmem".

These patches enable support for UFFDIO_ZEROPAGE for shared memory.

The first two patches are not strictly related to userfaultfd, they are
just minor refactoring to reduce amount of code duplication.

This patch (of 7):

Currently we update inode and shmem_inode_info before verifying that
used_blocks will not exceed max_blocks.  In case it will, we undo the
update.  Let's switch the order and move the verification of the blocks
count before the inode and shmem_inode_info update.

Link: http://lkml.kernel.org/r/1497939652-16528-2-git-send-email-rppt@linux.vnet.ibm.com


Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent fe490cc0

mm/shmem.c

+12 −13

Original line number	Diff line number	Diff line
		@@ -266,6 +266,14 @@ bool shmem_charge(struct inode *inode, long pages)

		if (shmem_acct_block(info->flags, pages))
		return false;

		if (sbinfo->max_blocks) {
		if (percpu_counter_compare(&sbinfo->used_blocks,
		sbinfo->max_blocks - pages) > 0)
		goto unacct;
		percpu_counter_add(&sbinfo->used_blocks, pages);
		}

		spin_lock_irqsave(&info->lock, flags);
		info->alloced += pages;
		inode->i_blocks += pages * BLOCKS_PER_PAGE;
		@@ -273,21 +281,12 @@ bool shmem_charge(struct inode *inode, long pages)
		spin_unlock_irqrestore(&info->lock, flags);
		inode->i_mapping->nrpages += pages;

		if (!sbinfo->max_blocks)
		return true;
		if (percpu_counter_compare(&sbinfo->used_blocks,
		sbinfo->max_blocks - pages) > 0) {
		inode->i_mapping->nrpages -= pages;
		spin_lock_irqsave(&info->lock, flags);
		info->alloced -= pages;
		shmem_recalc_inode(inode);
		spin_unlock_irqrestore(&info->lock, flags);

		unacct:
		shmem_unacct_blocks(info->flags, pages);
		return false;
		}
		percpu_counter_add(&sbinfo->used_blocks, pages);
		return true;
		}

		void shmem_uncharge(struct inode *inode, long pages)
		{