On 3/11/20 11:34 AM, Jason Gunthorpe wrote:
From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Many of the direct returns of error skipped doing the pte_unmap(). All non
zero exit paths must unmap the pte.
The pte_unmap() is split unnaturally like this because some of the error
exit paths trigger a sleep and must release the lock before sleeping.
Fixes: 992de9a8b751 ("mm/hmm: allow to mirror vma of a file on a DAX backed filesystem")
Fixes: 53f5c3f489ec ("mm/hmm: factor out pte and pmd handling to simplify hmm_vma_walk_pmd()")
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
The changes look OK to me but one issue noted below.
In any case, you can add:
Reviewed-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
---
mm/hmm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/mm/hmm.c b/mm/hmm.c
index 72e5a6d9a41756..35f85424176d14 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -325,6 +325,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
}
/* Report error for everything else */
+ pte_unmap(ptep);
*pfn = range->values[HMM_PFN_ERROR];
return -EFAULT;
} else {
@@ -339,10 +340,13 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
if (pte_devmap(pte)) {
hmm_vma_walk->pgmap = get_dev_pagemap(pte_pfn(pte),
hmm_vma_walk->pgmap);
- if (unlikely(!hmm_vma_walk->pgmap))
+ if (unlikely(!hmm_vma_walk->pgmap)) {
+ pte_unmap(ptep);
return -EBUSY;
+ }
} else if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pte_special(pte)) {
if (!is_zero_pfn(pte_pfn(pte))) {
+ pte_unmap(ptep);
*pfn = range->values[HMM_PFN_SPECIAL];
return -EFAULT;
}
@@ -437,7 +441,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, &pfns[i]);
if (r) {
- /* hmm_vma_handle_pte() did unmap pte directory */
+ /* hmm_vma_handle_pte() did pte_unmap() */
hmm_vma_walk->last = addr;
return r;
}
I think there is a case where hmm_vma_handle_pte() is called, a fault is requested,
pte_unmap() and hmm_vma_walk_hole_() are called, the latter returns zero (the fault
was handled OK), but now the page table is unmapped for successive loop iterations
and pte_unmap(ptep - 1) is called at the loop end.
Since this isn't an issue on x86_64 but is on x86_32, I can see how it could be missed.
