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as-iosched: fix double locking bug in as_merged_requests()

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If the two requests belong to the same io context, we will attempt
to lock the same lock twice. But swapping contexts is pointless in
that case, so just check for rioc == nioc before doing the double
lock and copy.

Tested-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-01-29 22:25:18 +01:00
parent 5b10ca19ea
commit 149a051f82
1 changed files with 7 additions and 3 deletions
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10
block/as-iosched.c
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@ -1275,9 +1275,13 @@ static void as_merged_requests(struct request_queue *q, struct request *req,
* Don't copy here but swap, because when anext is
* removed below, it must contain the unused context
*/
double_spin_lock(&rioc->lock, &nioc->lock, rioc < nioc);
swap_io_context(&rioc, &nioc);
double_spin_unlock(&rioc->lock, &nioc->lock, rioc < nioc);
if (rioc != nioc) {
double_spin_lock(&rioc->lock, &nioc->lock,
rioc < nioc);
swap_io_context(&rioc, &nioc);
double_spin_unlock(&rioc->lock, &nioc->lock,
rioc < nioc);
}
}
}