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

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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/[email protected]
Signed-off-by: Mike Rapoport <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Mike Rapoport 2017-09-06 16:22:56 -07:00 • committed by Linus Torvalds
commit b1cc94ab2f
1 changed files with 12 additions and 13 deletions
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25
mm/shmem.c
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@ -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;
@ -273,20 +281,11 @@ 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);
shmem_unacct_blocks(info->flags, pages);
return false;
}
percpu_counter_add(&sbinfo->used_blocks, pages);
return true;
unacct:
shmem_unacct_blocks(info->flags, pages);
return false;
}
void shmem_uncharge(struct inode *inode, long pages)