On Wed, 11 Dec 2013 16:58:19 +0000 David Vrabel <david.vrabel@xxxxxxxxxx> wrote: > Andrew, > > Dietmar Hahn reported an issue where calling vunmap() on a large (50 GB) > region would trigger soft lockup warnings. > > The following patch would resolve this (by adding a cond_resched() call > to vunmap_pmd_range()). Almost calls of vunmap(), unmap_kernel_range() > are from process context (as far as I could tell) except for an ACPI > driver (drivers/acpi/apei/ghes.c) calls unmap_kernel_range_noflush() > from an interrupt and NMI contexts. > > Can you advise on a preferred solution? > > For example, an unmap_kernel_page() function (callable from atomic > context) could be provided since the GHES driver only maps/unmaps a > single page. > > 8<------------------------- > mm/vmalloc: avoid soft lockup warnings when vunmap()'ing large ranges > > From: David Vrabel <david.vrabel@xxxxxxxxxx> > > If vunmap() is used to unmap a large (e.g., 50 GB) region, it may take > sufficiently long that it triggers soft lockup warnings. > > Add a cond_resched() into vunmap_pmd_range() so the calling task may > be resheduled after unmapping each PMD entry. This is how > zap_pmd_range() fixes the same problem for userspace mappings. > > ... > > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -75,6 +75,7 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long > addr, unsigned long end) > if (pmd_none_or_clear_bad(pmd)) > continue; > vunmap_pte_range(pmd, addr, next); > + cond_resched(); > } while (pmd++, addr = next, addr != end); > } Well that's ugly. We could redo unmap_kernel_range() so it takes an `atomic' flag then loops around unmapping N MB at a time, doing if (!atomic) cond_resched() each time. But that would require difficult tuning of N. I suppose we could just do if (!in_interrupt()) cond_resched(); in vunmap_pmd_range(), but that's pretty specific to ghes.c and doesn't permit unmap-inside-spinlock. So I can't immediately think of a suitable fix apart from adding a new unmap_kernel_range_atomic(). Then add a `bool atomic' arg to vunmap_page_range() and pass that all the way down. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
