On Fri, Feb 01, 2008 at 12:39:27PM -0500, Kiyoshi Ueda wrote:
<snip>
> > > end_that_request_last() is not called when __blk_end_reuqest()
> > > returns 1. Then, the issuer isn't waken up.
> > > So I think the BUG() or error messages should be there.
> >
> > you mean, end_that_request_last() isn't called when __end_that_request_first()
> > returns an error and this is the case only for fs and pc requests.
> > Otherwise it _is_ called, thus simulating somewhat the previous behavior.
> > However, we never BUG()'ged on residual byte counts before and
> > this driver has been in the kernel tree for ages, so what puzzles
> > me now is how is BUG()'ing here better than before and shouldn't we
> > simply issue a warning instead of killing the interrupt handler...
>
> The Jens' patch passes the residual byte counts to __blk_end_request(),
> so __end_that_reqeust_first() should never return 1 and we should never
> BUG() on the residual byte counts, unless inconsistency happens such as
> the size of remaining bios is bigger than the residual byte counts.
yep.
> So if __blk_end_request() returns 1 even with the Jens' patch,
> it means that the block layer or the driver really have a bug.
> And then, the request and the bios could leak or the issuer
> would wait forever because end_that_request_last() isn't called.
>
> The previous behavior might ignore such inconsistency and leak only
> the bios because it was calling end_that_request_last() anyway.
> I would like to BUG() in such cases personally, but I don't object
> strongly if you prefer not to BUG().
BUG() is definitely what we should do here to catch this case of sizeof(bios) >
rq->data_len. Putting a brown paper bag over the issue will never get it fixed
if it really leaks bios. Thanks for clarifying that.
By the way, shouldn't we be doing a little branch prediction here:
diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
index 74c6087..bee05a3 100644
--- a/drivers/ide/ide-cd.c
+++ b/drivers/ide/ide-cd.c
@@ -1722,7 +1722,7 @@ static ide_startstop_t cdrom_newpc_intr(ide_drive_t *drive)
*/
if ((stat & DRQ_STAT) == 0) {
spin_lock_irqsave(&ide_lock, flags);
- if (__blk_end_request(rq, 0, 0))
+ if (unlikely(__blk_end_request(rq, 0, rq->data_len)))
BUG();
HWGROUP(drive)->rq = NULL;
spin_unlock_irqrestore(&ide_lock, flags);
--
Regards/Gruß,
Boris.
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