| Message ID | 5d9a59eee6498ae017cc87d89aa723de7179f75d.1729858176.git.lorenzo.stoakes@oracle.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | fix error handling in mmap_region() and refactor | expand |
On 10/25/24 14:26, Lorenzo Stoakes wrote: > The only place where this was used was in mmap_region(), which we have now > adjusted to not require this to be performed (we reset ourselves in > effect). > > It also created a dangerous assumption that VMG state could be safely > reused after a merge, at which point it may have been mutated in unexpected > ways, leading to subtle bugs. > > Note that it was discovered by Wei Yang that there was also an error in > this code - we are comparing vmg->vma with prev after setting it to > NULL. > > This however had no impact, as we previously reset VMA iterator state > before attempting merge again, but it was useless effort. > > In any case, this patch removes all of the logic so also eliminates this > wasted effort. > > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Yeah glad to be rid of this. Reviewed-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/vma.c | 11 ----------- > 1 file changed, 11 deletions(-) > > diff --git a/mm/vma.c b/mm/vma.c > index b91c947babd6..7c690be67910 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -963,7 +963,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) > struct vm_area_struct *next = vmg->next; > unsigned long start = vmg->start; > unsigned long end = vmg->end; > - pgoff_t pgoff = vmg->pgoff; > pgoff_t pglen = PHYS_PFN(end - start); > bool can_merge_left, can_merge_right; > bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND; > @@ -1020,16 +1019,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) > return vmg->vma; > } > > - /* If expansion failed, reset state. Allows us to retry merge later. */ > - if (!just_expand) { > - vmg->vma = NULL; > - vmg->start = start; > - vmg->end = end; > - vmg->pgoff = pgoff; > - if (vmg->vma == prev) > - vma_iter_set(vmg->vmi, start); > - } > - > return NULL; > } >
diff --git a/mm/vma.c b/mm/vma.c index b91c947babd6..7c690be67910 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -963,7 +963,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) struct vm_area_struct *next = vmg->next; unsigned long start = vmg->start; unsigned long end = vmg->end; - pgoff_t pgoff = vmg->pgoff; pgoff_t pglen = PHYS_PFN(end - start); bool can_merge_left, can_merge_right; bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND; @@ -1020,16 +1019,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) return vmg->vma; } - /* If expansion failed, reset state. Allows us to retry merge later. */ - if (!just_expand) { - vmg->vma = NULL; - vmg->start = start; - vmg->end = end; - vmg->pgoff = pgoff; - if (vmg->vma == prev) - vma_iter_set(vmg->vmi, start); - } - return NULL; }
The only place where this was used was in mmap_region(), which we have now adjusted to not require this to be performed (we reset ourselves in effect). It also created a dangerous assumption that VMG state could be safely reused after a merge, at which point it may have been mutated in unexpected ways, leading to subtle bugs. Note that it was discovered by Wei Yang that there was also an error in this code - we are comparing vmg->vma with prev after setting it to NULL. This however had no impact, as we previously reset VMA iterator state before attempting merge again, but it was useless effort. In any case, this patch removes all of the logic so also eliminates this wasted effort. Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> --- mm/vma.c | 11 ----------- 1 file changed, 11 deletions(-)