[Xen-devel] [PATCHv2] mm/vmalloc: avoid soft lockup warnings when vunmap()'ing large ranges

[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.

All callers may sleep except for the APEI GHES driver (apei/ghes.c)
which calls unmap_kernel_range_no_flush() from NMI and IRQ contexts.
This driver only unmaps a single pages so don't call cond_resched() if
the unmap doesn't cross a PMD boundary.

Reported-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
v2: don't call cond_resched() at the end of a PMD range.
---
 mm/vmalloc.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0fdf968..1a8b162 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -75,6 +75,8 @@ 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);
+               if (next != end)
+                       cond_resched();
        } while (pmd++, addr = next, addr != end);
 }
 
-- 
1.7.2.5


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