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ext4: close race between direct IO and ext4_break_layouts()

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If the refcount of a page is lowered between the time that it is returned
by dax_busy_page() and when the refcount is again checked in
ext4_break_layouts() => ___wait_var_event(), the waiting function
ext4_wait_dax_page() will never be called.  This means that
ext4_break_layouts() will still have 'retry' set to false, so we'll stop
looping and never check the refcount of other pages in this inode.

Instead, always continue looping as long as dax_layout_busy_page() gives us
a page which it found with an elevated refcount.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
This commit is contained in:
Ross Zwisler 2018-09-11 13:31:16 -04:00 committed by Theodore Ts'o
parent 5f8c10936f
commit b1f382178d
1 changed files with 3 additions and 6 deletions
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9
fs/ext4/inode.c
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@ -4195,9 +4195,8 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
return 0;
}
static void ext4_wait_dax_page(struct ext4_inode_info *ei, bool *did_unlock)
static void ext4_wait_dax_page(struct ext4_inode_info *ei)
{
*did_unlock = true;
up_write(&ei->i_mmap_sem);
schedule();
down_write(&ei->i_mmap_sem);
@ -4207,14 +4206,12 @@ int ext4_break_layouts(struct inode *inode)
{
struct ext4_inode_info *ei = EXT4_I(inode);
struct page *page;
bool retry;
int error;
if (WARN_ON_ONCE(!rwsem_is_locked(&ei->i_mmap_sem)))
return -EINVAL;
do {
retry = false;
page = dax_layout_busy_page(inode->i_mapping);
if (!page)
return 0;
@ -4222,8 +4219,8 @@ int ext4_break_layouts(struct inode *inode)
error = ___wait_var_event(&page->_refcount,
atomic_read(&page->_refcount) == 1,
TASK_INTERRUPTIBLE, 0, 0,
ext4_wait_dax_page(ei, &retry));
} while (error == 0 && retry);
ext4_wait_dax_page(ei));
} while (error == 0);
return error;
}