Messages in this thread | | | From | Kevin Corry <> | Subject | Re: [PATCH] dm.c - device-mapper I/O path fixes | Date | Wed, 11 Dec 2002 08:02:24 -0600 |
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On Wednesday 11 December 2002 13:19, Denis Vlasenko wrote: > On 11 December 2002 11:16, Kevin Corry wrote: > > > > --- diff/drivers/md/dm.c 2002-12-11 12:00:29.000000000 +0000 > > > > +++ source/drivers/md/dm.c 2002-12-11 12:00:34.000000000 +0000 > > > > @@ -238,10 +238,11 @@ > > > > static spinlock_t _uptodate_lock = SPIN_LOCK_UNLOCKED; > > > > unsigned long flags; > > > > > > > > - spin_lock_irqsave(&_uptodate_lock, flags); > > > > - if (error) > > > > + if (error) { > > > > + spin_lock_irqsave(&_uptodate_lock, flags); > > > > io->error = error; > > > > - spin_unlock_irqrestore(&_uptodate_lock, flags); > > > > + spin_unlock_irqrestore(&_uptodate_lock, flags); > > > > + } > > > > > > > > if (atomic_dec_and_test(&io->io_count)) { > > > > if (atomic_dec_and_test(&io->md->pending)) > > > > > > This seems pointless, end result: > > > > > > spin_lock_irqsave(&_uptodate_lock, flags); > > > io->error = error; > > > spin_unlock_irqrestore(&_uptodate_lock, flags); > > > > Are you saying the "if (error)" part is pointless? If so, I have to > > No. Locking is pointless. What exactly you try to protect here?
The "struct dm_io *io" that is passed to dec_pending() can be accessed by multiple threads at the same time, thus some form of locking is required.
I had been thinking about whether the "error" field could be an atomic_t, which would remove the requirement for the spinlock in dec_pending(). However, I don't know how atomic_t's behave with negative values. I know atomic_t's are only guaranteed to have 24-bits of precision, yet all arch's define atomic_t with a signed integer. Can anyone enlighten me on this?
Perhaps we could make "error" and atomic_t, and store the absolute-value of the error code, and always return -error in the bio_endio() call. Or is that just too ugly?
-- Kevin Corry corryk@us.ibm.com http://evms.sourceforge.net/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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