Messages in this thread |  | | Date | Thu, 13 Mar 2003 10:26:01 +0100 | From | Jens Axboe <> | Subject | Re: [PATCH] bug in 2.4 bh_kmap_irq() breaks IDE under preempt patch |
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On Wed, Mar 12 2003, Joe Korty wrote: > Hi Alan, Everyone, > The bh_map_irq/bh_unmap_irq functions are broken in 2.4.21-pre5. > However no symptoms occur unless the preemption patch is applied. > > The bug is that bh_map_irq *conditionally* calls kmap_atomic (which > disables preemption as one of its functions), while bh_unmap_irq > *unconditionally* calls kunmap_atomic (which enables it). This > imbalance results in a occasional off-by-one preempt_count, which in > turn causes IDE PIO mode interrupt code (specifically, read_intr) to > erronously invoke preempt_schedule while at interrupt level. > > The below patch compiles and boots ide=nodma on my preempt 2.4 kernel > on the one motherboard that had the problem. Before this patch, the > kernel would not even boot for that motherboard. I also applied and > test booted a pure 2.4.21-pre5 kernel with this patch. > > The patch implements my preference for simplicity, so you may want to > take some other approach if maximal performance is what you want.
I fixed this in 2.5 ages ago, just didn't get it in 2.4 block-highmem... There's a tiny bit missing from your patch:
> --- include/linux/highmem.h.orig 2003-03-12 05:01:56.000000000 -0500 > +++ include/linux/highmem.h 2003-03-12 16:07:04.000000000 -0500 > @@ -33,22 +33,10 @@ > { > unsigned long addr; > > - __save_flags(*flags); > - > - /* > - * could be low > - */ > - if (!PageHighMem(bh->b_page)) > - return bh->b_data; > - > - /* > - * it's a highmem page > - */ > - __cli(); > + local_irq_save(*flags); local_irq_disable();
> addr = (unsigned long) kmap_atomic(bh->b_page, KM_BH_IRQ); > > - if (addr & ~PAGE_MASK) > - BUG(); > + BUG_ON (addr & ~PAGE_MASK); > > return (char *) addr + bh_offset(bh); > } > @@ -58,7 +46,7 @@ > unsigned long ptr = (unsigned long) buffer & PAGE_MASK; > > kunmap_atomic((void *) ptr, KM_BH_IRQ); > - __restore_flags(*flags); > + local_irq_restore(*flags); > }
other than that it's fine. See 2.5 for reference.
-- Jens Axboe
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