Messages in this thread | | | Date | Thu, 13 May 2010 08:41:00 -0400 | From | Andrew Morton <> | Subject | Re: [PATCH 4/4] Btrfs: add basic DIO read/write support V3 |
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On Thu, 13 May 2010 11:31:45 -0400 Josef Bacik <josef@redhat.com> wrote:
> On Thu, May 13, 2010 at 11:14:30AM -0400, Christoph Hellwig wrote: > > On Wed, May 12, 2010 at 04:40:53PM -0400, Josef Bacik wrote: > > > V1->V2 > > > -Use __blockdev_direct_IO instead of helper > > > -Use KM_IRQ0 for kmap instead of KM_USER0 > > > > I still don't think this is correct. The completion can come from > > softirq and hardirq context, and possibly even normal process context. > > You either need to check for all these, or you need to use the generic > > complete in user context helper btrfs has available for other types > > of I/O. > > > > AIO's aio_complete does kmap with KM_IRQ0/1 and it gets called in the same > context as the btrfs completion handler, so if it's ok for aio_complete it > should be ok for btrfs right? Thanks, >
Using KM_USERx from irq context is a horrid, horrid bug.
Using KM_IRQx with local interrupts enabled is a ditto.
It's OK to use KM_IRQx from process context as long as local interrupts are disabled.
kmap slots are just per-cpu variables. Each one has a particular usage convention: process-context-only, must-be-irq-safe, etc.
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