diff options
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/userfaultfd.c | 13 | ||||
| -rw-r--r-- | mm/vma.c | 51 | ||||
| -rw-r--r-- | mm/vma.h | 9 |
3 files changed, 66 insertions, 7 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index fbf2cf62ab9f..7d5d709cc838 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1902,6 +1902,14 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, unsigned long end) { struct vm_area_struct *ret; + bool give_up_on_oom = false; + + /* + * If we are modifying only and not splitting, just give up on the merge + * if OOM prevents us from merging successfully. + */ + if (start == vma->vm_start && end == vma->vm_end) + give_up_on_oom = true; /* Reset ptes for the whole vma range if wr-protected */ if (userfaultfd_wp(vma)) @@ -1909,7 +1917,7 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, ret = vma_modify_flags_uffd(vmi, prev, vma, start, end, vma->vm_flags & ~__VM_UFFD_FLAGS, - NULL_VM_UFFD_CTX); + NULL_VM_UFFD_CTX, give_up_on_oom); /* * In the vma_merge() successful mprotect-like case 8: @@ -1960,7 +1968,8 @@ int userfaultfd_register_range(struct userfaultfd_ctx *ctx, new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags; vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end, new_flags, - (struct vm_userfaultfd_ctx){ctx}); + (struct vm_userfaultfd_ctx){ctx}, + /* give_up_on_oom = */false); if (IS_ERR(vma)) return PTR_ERR(vma); @@ -666,6 +666,9 @@ static void vmg_adjust_set_range(struct vma_merge_struct *vmg) /* * Actually perform the VMA merge operation. * + * IMPORTANT: We guarantee that, should vmg->give_up_on_oom is set, to not + * modify any VMAs or cause inconsistent state should an OOM condition arise. + * * Returns 0 on success, or an error value on failure. */ static int commit_merge(struct vma_merge_struct *vmg) @@ -685,6 +688,12 @@ static int commit_merge(struct vma_merge_struct *vmg) init_multi_vma_prep(&vp, vma, vmg); + /* + * If vmg->give_up_on_oom is set, we're safe, because we don't actually + * manipulate any VMAs until we succeed at preallocation. + * + * Past this point, we will not return an error. + */ if (vma_iter_prealloc(vmg->vmi, vma)) return -ENOMEM; @@ -915,7 +924,13 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( if (anon_dup) unlink_anon_vmas(anon_dup); - vmg->state = VMA_MERGE_ERROR_NOMEM; + /* + * We've cleaned up any cloned anon_vma's, no VMAs have been + * modified, no harm no foul if the user requests that we not + * report this and just give up, leaving the VMAs unmerged. + */ + if (!vmg->give_up_on_oom) + vmg->state = VMA_MERGE_ERROR_NOMEM; return NULL; } @@ -926,7 +941,15 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( abort: vma_iter_set(vmg->vmi, start); vma_iter_load(vmg->vmi); - vmg->state = VMA_MERGE_ERROR_NOMEM; + + /* + * This means we have failed to clone anon_vma's correctly, but no + * actual changes to VMAs have occurred, so no harm no foul - if the + * user doesn't want this reported and instead just wants to give up on + * the merge, allow it. + */ + if (!vmg->give_up_on_oom) + vmg->state = VMA_MERGE_ERROR_NOMEM; return NULL; } @@ -1068,6 +1091,10 @@ int vma_expand(struct vma_merge_struct *vmg) /* This should already have been checked by this point. */ VM_WARN_ON_VMG(!can_merge_remove_vma(next), vmg); vma_start_write(next); + /* + * In this case we don't report OOM, so vmg->give_up_on_mm is + * safe. + */ ret = dup_anon_vma(middle, next, &anon_dup); if (ret) return ret; @@ -1090,9 +1117,15 @@ int vma_expand(struct vma_merge_struct *vmg) return 0; nomem: - vmg->state = VMA_MERGE_ERROR_NOMEM; if (anon_dup) unlink_anon_vmas(anon_dup); + /* + * If the user requests that we just give upon OOM, we are safe to do so + * here, as commit merge provides this contract to us. Nothing has been + * changed - no harm no foul, just don't report it. + */ + if (!vmg->give_up_on_oom) + vmg->state = VMA_MERGE_ERROR_NOMEM; return -ENOMEM; } @@ -1534,6 +1567,13 @@ static struct vm_area_struct *vma_modify(struct vma_merge_struct *vmg) if (vmg_nomem(vmg)) return ERR_PTR(-ENOMEM); + /* + * Split can fail for reasons other than OOM, so if the user requests + * this it's probably a mistake. + */ + VM_WARN_ON(vmg->give_up_on_oom && + (vma->vm_start != start || vma->vm_end != end)); + /* Split any preceding portion of the VMA. */ if (vma->vm_start < start) { int err = split_vma(vmg->vmi, vma, start, 1); @@ -1602,12 +1642,15 @@ struct vm_area_struct struct vm_area_struct *vma, unsigned long start, unsigned long end, unsigned long new_flags, - struct vm_userfaultfd_ctx new_ctx) + struct vm_userfaultfd_ctx new_ctx, + bool give_up_on_oom) { VMG_VMA_STATE(vmg, vmi, prev, vma, start, end); vmg.flags = new_flags; vmg.uffd_ctx = new_ctx; + if (give_up_on_oom) + vmg.give_up_on_oom = true; return vma_modify(&vmg); } @@ -114,6 +114,12 @@ struct vma_merge_struct { */ bool just_expand :1; + /* + * If a merge is possible, but an OOM error occurs, give up and don't + * execute the merge, returning NULL. + */ + bool give_up_on_oom :1; + /* Internal flags set during merge process: */ /* @@ -255,7 +261,8 @@ __must_check struct vm_area_struct struct vm_area_struct *vma, unsigned long start, unsigned long end, unsigned long new_flags, - struct vm_userfaultfd_ctx new_ctx); + struct vm_userfaultfd_ctx new_ctx, + bool give_up_on_oom); __must_check struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg); |