The patch titled
Subject: mm: pagewalk: make error checks more obvious
has been added to the -mm mm-unstable branch. Its filename is
mm-pagewalk-make-error-checks-more-obvious.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-pagewalk-make-error-checks-more-obvious.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Rolf Eike Beer <eb@xxxxxxxxx>
Subject: mm: pagewalk: make error checks more obvious
Date: Mon, 22 Aug 2022 15:00:05 +0200
Patch series "Minor improvements for pagewalk code".
For some project I had to use the pagewalk API for certain things and
during this have read through the code multiple times. Our usage has
changed several times depending on our current state of research as well.
During all of this I have made some tweaks to the code to be able to follow it
better when hunting my own problems, and not call into some things that I
actually don't need. The patches are more or less independent of each other.
This patch (of 6):
The err variable only needs to be checked when it was assigned directly
before, it is not carried on to any later checks. Move the checks into
the same "if" conditions where they are assigned. Also just return the
error at the relevant places. While at it move these err variables to a
more local scope at some places.
Link: https://lkml.kernel.org/r/3200642.44csPzL39Z@devpool047
Link: https://lkml.kernel.org/r/2203731.iZASKD2KPV@devpool047
Signed-off-by: Rolf Eike Beer <eb@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/pagewalk.c | 140 ++++++++++++++++++++++++++----------------------
1 file changed, 77 insertions(+), 63 deletions(-)
--- a/mm/pagewalk.c~mm-pagewalk-make-error-checks-more-obvious
+++ a/mm/pagewalk.c
@@ -24,25 +24,24 @@ static int walk_pte_range_inner(pte_t *p
unsigned long end, struct mm_walk *walk)
{
const struct mm_walk_ops *ops = walk->ops;
- int err = 0;
for (;;) {
- err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
+ int err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
if (err)
- break;
+ return err;
if (addr >= end - PAGE_SIZE)
break;
addr += PAGE_SIZE;
pte++;
}
- return err;
+ return 0;
}
static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
pte_t *pte;
- int err = 0;
+ int err;
spinlock_t *ptl;
if (walk->no_vma) {
@@ -62,7 +61,6 @@ static int walk_pte_range(pmd_t *pmd, un
static int walk_hugepd_range(hugepd_t *phpd, unsigned long addr,
unsigned long end, struct mm_walk *walk, int pdshift)
{
- int err = 0;
const struct mm_walk_ops *ops = walk->ops;
int shift = hugepd_shift(*phpd);
int page_size = 1 << shift;
@@ -75,6 +73,7 @@ static int walk_hugepd_range(hugepd_t *p
for (;;) {
pte_t *pte;
+ int err;
spin_lock(&walk->mm->page_table_lock);
pte = hugepte_offset(*phpd, addr, pdshift);
@@ -82,12 +81,12 @@ static int walk_hugepd_range(hugepd_t *p
spin_unlock(&walk->mm->page_table_lock);
if (err)
- break;
+ return err;
if (addr >= end - page_size)
break;
addr += page_size;
}
- return err;
+ return 0;
}
#else
static int walk_hugepd_range(hugepd_t *phpd, unsigned long addr,
@@ -103,18 +102,20 @@ static int walk_pmd_range(pud_t *pud, un
pmd_t *pmd;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
- int err = 0;
int depth = real_depth(3);
pmd = pmd_offset(pud, addr);
do {
-again:
+ int err;
+
+ again:
next = pmd_addr_end(addr, end);
if (pmd_none(*pmd) || (!walk->vma && !walk->no_vma)) {
- if (ops->pte_hole)
+ if (ops->pte_hole) {
err = ops->pte_hole(addr, next, depth, walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
continue;
}
@@ -124,10 +125,11 @@ again:
* This implies that each ->pmd_entry() handler
* needs to know about pmd_trans_huge() pmds
*/
- if (ops->pmd_entry)
+ if (ops->pmd_entry) {
err = ops->pmd_entry(pmd, addr, next, walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
if (walk->action == ACTION_AGAIN)
goto again;
@@ -152,10 +154,10 @@ again:
else
err = walk_pte_range(pmd, addr, next, walk);
if (err)
- break;
+ return err;
} while (pmd++, addr = next, addr != end);
- return err;
+ return 0;
}
static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
@@ -164,27 +166,30 @@ static int walk_pud_range(p4d_t *p4d, un
pud_t *pud;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
- int err = 0;
int depth = real_depth(2);
pud = pud_offset(p4d, addr);
do {
+ int err;
+
again:
next = pud_addr_end(addr, end);
if (pud_none(*pud) || (!walk->vma && !walk->no_vma)) {
- if (ops->pte_hole)
+ if (ops->pte_hole) {
err = ops->pte_hole(addr, next, depth, walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
continue;
}
walk->action = ACTION_SUBTREE;
- if (ops->pud_entry)
+ if (ops->pud_entry) {
err = ops->pud_entry(pud, addr, next, walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
if (walk->action == ACTION_AGAIN)
goto again;
@@ -204,10 +209,10 @@ static int walk_pud_range(p4d_t *p4d, un
else
err = walk_pmd_range(pud, addr, next, walk);
if (err)
- break;
+ return err;
} while (pud++, addr = next, addr != end);
- return err;
+ return 0;
}
static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
@@ -216,33 +221,35 @@ static int walk_p4d_range(pgd_t *pgd, un
p4d_t *p4d;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
- int err = 0;
int depth = real_depth(1);
p4d = p4d_offset(pgd, addr);
do {
+ int err;
+
next = p4d_addr_end(addr, end);
if (p4d_none_or_clear_bad(p4d)) {
- if (ops->pte_hole)
+ if (ops->pte_hole) {
err = ops->pte_hole(addr, next, depth, walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
continue;
}
if (ops->p4d_entry) {
err = ops->p4d_entry(p4d, addr, next, walk);
if (err)
- break;
+ return err;
}
if (is_hugepd(__hugepd(p4d_val(*p4d))))
err = walk_hugepd_range((hugepd_t *)p4d, addr, next, walk, P4D_SHIFT);
else if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)
err = walk_pud_range(p4d, addr, next, walk);
if (err)
- break;
+ return err;
} while (p4d++, addr = next, addr != end);
- return err;
+ return 0;
}
static int walk_pgd_range(unsigned long addr, unsigned long end,
@@ -251,35 +258,37 @@ static int walk_pgd_range(unsigned long
pgd_t *pgd;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
- int err = 0;
if (walk->pgd)
pgd = walk->pgd + pgd_index(addr);
else
pgd = pgd_offset(walk->mm, addr);
do {
+ int err;
+
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd)) {
- if (ops->pte_hole)
+ if (ops->pte_hole) {
err = ops->pte_hole(addr, next, 0, walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
continue;
}
if (ops->pgd_entry) {
err = ops->pgd_entry(pgd, addr, next, walk);
if (err)
- break;
+ return err;
}
if (is_hugepd(__hugepd(pgd_val(*pgd))))
err = walk_hugepd_range((hugepd_t *)pgd, addr, next, walk, PGDIR_SHIFT);
else if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry || ops->pte_entry)
err = walk_p4d_range(pgd, addr, next, walk);
if (err)
- break;
+ return err;
} while (pgd++, addr = next, addr != end);
- return err;
+ return 0;
}
#ifdef CONFIG_HUGETLB_PAGE
@@ -300,9 +309,10 @@ static int walk_hugetlb_range(unsigned l
unsigned long sz = huge_page_size(h);
pte_t *pte;
const struct mm_walk_ops *ops = walk->ops;
- int err = 0;
do {
+ int err;
+
next = hugetlb_entry_end(h, addr, end);
pte = huge_pte_offset(walk->mm, addr & hmask, sz);
@@ -312,10 +322,10 @@ static int walk_hugetlb_range(unsigned l
err = ops->pte_hole(addr, next, -1, walk);
if (err)
- break;
+ return err;
} while (addr = next, addr != end);
- return err;
+ return 0;
}
#else /* CONFIG_HUGETLB_PAGE */
@@ -351,10 +361,13 @@ static int walk_page_test(unsigned long
* vma(VM_PFNMAP).
*/
if (vma->vm_flags & VM_PFNMAP) {
- int err = 1;
- if (ops->pte_hole)
- err = ops->pte_hole(start, end, -1, walk);
- return err ? err : 1;
+ if (ops->pte_hole) {
+ int err = ops->pte_hole(start, end, -1, walk);
+
+ return err ? err : 1;
+ }
+
+ return 1;
}
return 0;
}
@@ -428,7 +441,6 @@ int walk_page_range(struct mm_struct *mm
unsigned long end, const struct mm_walk_ops *ops,
void *private)
{
- int err = 0;
unsigned long next;
struct vm_area_struct *vma;
struct mm_walk walk = {
@@ -447,6 +459,8 @@ int walk_page_range(struct mm_struct *mm
vma = find_vma(walk.mm, start);
do {
+ int err;
+
if (!vma) { /* after the last vma */
walk.vma = NULL;
next = end;
@@ -465,18 +479,18 @@ int walk_page_range(struct mm_struct *mm
* controlling the pagewalk, so should never
* be passed to the callers.
*/
- err = 0;
continue;
}
if (err < 0)
- break;
+ return err;
}
- if (walk.vma || walk.ops->pte_hole)
+ if (walk.vma || walk.ops->pte_hole) {
err = __walk_page_range(start, next, &walk);
- if (err)
- break;
+ if (err)
+ return err;
+ }
} while (start = next, start < end);
- return err;
+ return 0;
}
/*
@@ -571,11 +585,12 @@ int walk_page_mapping(struct address_spa
struct vm_area_struct *vma;
pgoff_t vba, vea, cba, cea;
unsigned long start_addr, end_addr;
- int err = 0;
lockdep_assert_held(&mapping->i_mmap_rwsem);
vma_interval_tree_foreach(vma, &mapping->i_mmap, first_index,
first_index + nr - 1) {
+ int err;
+
/* Clip to the vma */
vba = vma->vm_pgoff;
vea = vba + vma_pages(vma);
@@ -593,16 +608,15 @@ int walk_page_mapping(struct address_spa
walk.mm = vma->vm_mm;
err = walk_page_test(vma->vm_start, vma->vm_end, &walk);
- if (err > 0) {
- err = 0;
- break;
- } else if (err < 0)
- break;
+ if (err > 0)
+ return 0;
+ else if (err < 0)
+ return err;
err = __walk_page_range(start_addr, end_addr, &walk);
if (err)
- break;
+ return err;
}
- return err;
+ return 0;
}
_
Patches currently in -mm which might be from eb@xxxxxxxxx are
mm-pagewalk-make-error-checks-more-obvious.patch
mm-pagewalk-dont-check-vma-in-walk_page_range_novma.patch
mm-pagewalk-fix-documentation-of-pte-hole-handling.patch
mm-pagewalk-add-api-documentation-for-walk_page_range_novma.patch
mm-pagewalk-allow-walk_page_range_novma-without-mm.patch
mm-pagewalk-move-variables-to-more-local-scope-tweak-loops.patch
