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md/bitmap: always wait for writes on unplug.

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If two threads call bitmap_unplug at the same time, then
one might schedule all the writes, and the other might
decide that it doesn't need to wait.  But really it does.

It rarely hurts to wait when it isn't absolutely necessary,
and the current code doesn't really focus on 'absolutely necessary'
anyway.  So just wait always.

This can potentially lead to data corruption if a crash happens
at an awkward time and data was written before the bitmap was
updated.  It is very unlikely, but this should go to -stable
just to be safe.  Appropriate for any -stable.

Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@vger.kernel.org (please delay until 3.18 is released)
This commit is contained in:
NeilBrown 2014-09-09 14:13:51 +10:00
parent 8e0e99ba64
commit 4b5060ddae
1 changed files with 6 additions and 10 deletions
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6
drivers/md/bitmap.c
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@ -879,7 +879,6 @@ void bitmap_unplug(struct bitmap *bitmap)
{
unsigned long i;
int dirty, need_write;
int wait = 0;
if (!bitmap || !bitmap->storage.filemap ||
test_bit(BITMAP_STALE, &bitmap->flags))
@ -897,16 +896,13 @@ void bitmap_unplug(struct bitmap *bitmap)
clear_page_attr(bitmap, i, BITMAP_PAGE_PENDING);
write_page(bitmap, bitmap->storage.filemap[i], 0);
}
if (dirty)
wait = 1;
}
if (wait) { /* if any writes were performed, we need to wait on them */
if (bitmap->storage.file)
wait_event(bitmap->write_wait,
atomic_read(&bitmap->pending_writes)==0);
else
md_super_wait(bitmap->mddev);
}
if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
bitmap_file_kick(bitmap);
}