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    SubjectRe: [PATCH] dm.c - device-mapper I/O path fixes
    Date
    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?

    > disagree. A bio may be split into several sub-bio's. When each of
    > those split bio's completes, they are going to call this function.
    > But if only one of those split bio's has an error, then the error
    > might get lost without that "if" statement.
    >
    > However, it might be a good idea to consider how bio's keep track of
    > errors. When a bio is created, it is marked UPTODATE. Then, if any
    > part of a bio takes an error, the UPTODATE flag is turned off. When
    > the whole bio completes, if the UPTODATE flag is still on, there were
    > no errors during the i/o. Perhaps the "error" field in "struct dm_io"
    > could be modified to use this method of error tracking? Then we could
    > change dec_pending() to be something like:
    >
    > if (error)
    > clear_bit(DM_IO_UPTODATE, &io->error);
    >
    > with a "set_bit(DM_IO_UPTODATE, &ci.io->error);" in __bio_split().

    You seem to overestimate my knowledge of this part of the kernel. :(
    --
    vda
    -
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