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Wed, 4 Mar 2026 16:51:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47629C4CEF7; Wed, 4 Mar 2026 16:51:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772643113; bh=ursMg6G23K3STjUq3+z/V1NN7ezRFAIkK7w5ZBPoihU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=V+GMIDGFl0STObezr020FXhXtNnmnK0c18C8KX5kHjtvlH0y3dcwZwSxAw1Q/jdWu QcBV7MFDhoZFHvvcYnwlToRXd1cBfqgDjxWzRseiX7EjDzZrzPy2ZWtR5kKBLmn+yi J51TuuGdE4/z9q6CGu1Xl7pWJNHUiJXwknoRuJfMCa/DgfhXI4SgmSKR1tnbUxCpUh xE4LAnDbbgl3eifLHPy1OoPLXyDWHq9KC8y2NhSfkDhDuIaMEH2Gvm5FBnmHrVIqhg 55VDYE2AOHQf0kN0SQsc/rhQxwzzOaw6Djy+Xt3L/1FnETcWtYTst56SAZsN2TAPcw LBapGd7hkfS0Q== Date: Wed, 4 Mar 2026 16:51:49 +0000 From: "Lorenzo Stoakes (Oracle)" To: Suren Baghdasaryan Cc: Lorenzo Stoakes , akpm@linux-foundation.org, willy@infradead.org, david@kernel.org, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@suse.cz, jannh@google.com, rppt@kernel.org, mhocko@suse.com, pfalcato@suse.de, kees@kernel.org, maddy@linux.ibm.com, npiggin@gmail.com, mpe@ellerman.id.au, chleroy@kernel.org, borntraeger@linux.ibm.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, svens@linux.ibm.com, gerald.schaefer@linux.ibm.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, "Ritesh Harjani (IBM)" Subject: Re: [PATCH v3 2/3] mm: replace vma_start_write() with vma_start_write_killable() Message-ID: <0433a4f0-d183-438f-8063-3e4425b14d77@lucifer.local> References: <20260226070609.3072570-1-surenb@google.com> <20260226070609.3072570-3-surenb@google.com> <74bffc7a-2b8c-40ae-ab02-cd0ced082e18@lucifer.local> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Mar 03, 2026 at 02:11:31PM -0800, Suren Baghdasaryan wrote: > On Mon, Mar 2, 2026 at 6:53 AM Lorenzo Stoakes > wrote: > > > > On Wed, Feb 25, 2026 at 11:06:08PM -0800, Suren Baghdasaryan wrote: > > > Now that we have vma_start_write_killable() we can replace most of the > > > vma_start_write() calls with it, improving reaction time to the kill > > > signal. > > > > > > There are several places which are left untouched by this patch: > > > > > > 1. free_pgtables() because function should free page tables even if a > > > fatal signal is pending. > > > > > > 2. process_vma_walk_lock(), which requires changes in its callers and > > > will be handled in the next patch. > > > > > > 3. userfaultd code, where some paths calling vma_start_write() can > > > handle EINTR and some can't without a deeper code refactoring. > > > > Surprise surprise :)) > > > > > > > > 4. mpol_rebind_mm() which is used by cpusset controller for migrations > > > > Incredibly nitty but cpusset -> cpuset? > > Ack. > > > > > > and operates on a remote mm. Incomplete operations here would result > > > in an inconsistent cgroup state. > > > > > > 5. vm_flags_{set|mod|clear} require refactoring that involves moving > > > vma_start_write() out of these functions and replacing it with > > > vma_assert_write_locked(), then callers of these functions should > > > lock the vma themselves using vma_start_write_killable() whenever > > > possible. > > > > This should be dealt with by my ongoing mmap_prepare, vma flags work. > > That would be great! It makes it much simpler once you are done with > that refactoring. Yeah will be a big series ;) stats++; > > > > > > > > > Suggested-by: Matthew Wilcox > > > Signed-off-by: Suren Baghdasaryan > > > Reviewed-by: Ritesh Harjani (IBM) # powerpc > > > > Overall I'm a little concerned about whether callers can handle -EINTR in all > > cases, have you checked? Might we cause some weirdness in userspace if a syscall > > suddenly returns -EINTR when before it didn't? > > I did check the kernel users and put the patchset through AI reviews. > I haven't checked if any of the affected syscalls do not advertise > -EINTR as a possible error. Adding that to my todo list for the next > respin. Ah yeah as per Matthew's, fair enough. And yes it's only fatal signals. But then is there any point in doing special handling/not filtering? We may as well not :) I also don't want us to run into an issue where something other than a fatal error results in an -EINTR. > > > > > Also maybe we should update the manpages to reflect this, as semi-usless as the > > 'possible error codes' sections are... > > Ok, I'll check which syscalls need to be updated and will note that in > cover letter. Once the patchset is accepted I'll update the manpages > for them. Yeah obv nop as per Matthew. > > > > > > --- > > > arch/powerpc/kvm/book3s_hv_uvmem.c | 5 +- > > > mm/khugepaged.c | 5 +- > > > mm/madvise.c | 4 +- > > > mm/memory.c | 2 + > > > mm/mempolicy.c | 8 ++- > > > mm/mlock.c | 21 +++++-- > > > mm/mprotect.c | 4 +- > > > mm/mremap.c | 4 +- > > > mm/vma.c | 93 +++++++++++++++++++++--------- > > > mm/vma_exec.c | 6 +- > > > 10 files changed, 109 insertions(+), 43 deletions(-) > > > > > > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c > > > index 5fbb95d90e99..0a28b48a46b8 100644 > > > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c > > > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c > > > @@ -410,7 +410,10 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm, > > > ret = H_STATE; > > > break; > > > } > > > - vma_start_write(vma); > > > + if (vma_start_write_killable(vma)) { > > > + ret = H_STATE; > > > + break; > > > + } > > > /* Copy vm_flags to avoid partial modifications in ksm_madvise */ > > > vm_flags = vma->vm_flags; > > > ret = ksm_madvise(vma, vma->vm_start, vma->vm_end, > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > index 1dd3cfca610d..6c92e31ee5fb 100644 > > > --- a/mm/khugepaged.c > > > +++ b/mm/khugepaged.c > > > @@ -1141,7 +1141,10 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a > > > if (result != SCAN_SUCCEED) > > > goto out_up_write; > > > /* check if the pmd is still valid */ > > > - vma_start_write(vma); > > > + if (vma_start_write_killable(vma)) { > > > + result = SCAN_FAIL; > > > + goto out_up_write; > > > + } > > > result = check_pmd_still_valid(mm, address, pmd); > > > if (result != SCAN_SUCCEED) > > > goto out_up_write; > > > diff --git a/mm/madvise.c b/mm/madvise.c > > > index c0370d9b4e23..ccdaea6b3b15 100644 > > > --- a/mm/madvise.c > > > +++ b/mm/madvise.c > > > @@ -173,7 +173,9 @@ static int madvise_update_vma(vm_flags_t new_flags, > > > madv_behavior->vma = vma; > > > > > > /* vm_flags is protected by the mmap_lock held in write mode. */ > > > - vma_start_write(vma); > > > + if (vma_start_write_killable(vma)) > > > + return -EINTR; > > > + > > > vm_flags_reset(vma, new_flags); > > > if (set_new_anon_name) > > > return replace_anon_vma_name(vma, anon_name); > > > diff --git a/mm/memory.c b/mm/memory.c > > > index 07778814b4a8..691062154cf5 100644 > > > --- a/mm/memory.c > > > +++ b/mm/memory.c > > > @@ -379,6 +379,8 @@ void free_pgd_range(struct mmu_gather *tlb, > > > * page tables that should be removed. This can differ from the vma mappings on > > > * some archs that may have mappings that need to be removed outside the vmas. > > > * Note that the prev->vm_end and next->vm_start are often used. > > > + * We don't use vma_start_write_killable() because page tables should be freed > > > + * even if the task is being killed. > > > * > > > * The vma_end differs from the pg_end when a dup_mmap() failed and the tree has > > > * unrelated data to the mm_struct being torn down. > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > > index 0e5175f1c767..90939f5bde02 100644 > > > --- a/mm/mempolicy.c > > > +++ b/mm/mempolicy.c > > > @@ -1784,7 +1784,8 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le > > > return -EINVAL; > > > if (end == start) > > > return 0; > > > - mmap_write_lock(mm); > > > + if (mmap_write_lock_killable(mm)) > > > + return -EINTR; > > > > Hmm mmap write lock as well now :) I guess it makes sense here, esp given mmap > > write lock part of VMA write lock. > > Yeah, I thought while we are at it we can make this part a bit better too... Yup that's fair. > > > > > > > > prev = vma_prev(&vmi); > > > for_each_vma_range(vmi, vma, end) { > > > /* > > > @@ -1801,13 +1802,16 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le > > > err = -EOPNOTSUPP; > > > break; > > > } > > > + if (vma_start_write_killable(vma)) { > > > + err = -EINTR; > > > + break; > > > + } > > > new = mpol_dup(old); > > > if (IS_ERR(new)) { > > > err = PTR_ERR(new); > > > break; > > > } > > > > > > - vma_start_write(vma); > > > > Are we ok with moving this to before mpol_dup()? Does this matter? Confused as > > to why you moved this up? > > I thought if locking fails, it would be better to check that earlier > before allocating a new mempolicy. That seems to be safe, but thinking > about this now, if allocation goes into direct reclaim and causes the > lock to be held for longer then that might not be such a hot idea... Yeah :) it's stuff like this that makes me worry. But moreso some horrendous lock ordering issue... > > > > > > new->home_node = home_node; > > > err = mbind_range(&vmi, vma, &prev, start, end, new); > > > mpol_put(new); > > > diff --git a/mm/mlock.c b/mm/mlock.c > > > index 2f699c3497a5..c562c77c3ee0 100644 > > > --- a/mm/mlock.c > > > +++ b/mm/mlock.c > > > @@ -420,7 +420,7 @@ static int mlock_pte_range(pmd_t *pmd, unsigned long addr, > > > * Called for mlock(), mlock2() and mlockall(), to set @vma VM_LOCKED; > > > * called for munlock() and munlockall(), to clear VM_LOCKED from @vma. > > > */ > > > > You should update the comment to reflect this possible return value. > > Ack. Thanks! > > > > > > -static void mlock_vma_pages_range(struct vm_area_struct *vma, > > > +static int mlock_vma_pages_range(struct vm_area_struct *vma, > > > unsigned long start, unsigned long end, vm_flags_t newflags) > > > { > > > static const struct mm_walk_ops mlock_walk_ops = { > > > @@ -441,7 +441,9 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma, > > > */ > > > if (newflags & VM_LOCKED) > > > newflags |= VM_IO; > > > - vma_start_write(vma); > > > + if (vma_start_write_killable(vma)) > > > + return -EINTR; > > > + > > > vm_flags_reset_once(vma, newflags); > > > > > > lru_add_drain(); > > > @@ -452,6 +454,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma, > > > newflags &= ~VM_IO; > > > vm_flags_reset_once(vma, newflags); > > > } > > > + return 0; > > > } > > > > > > /* > > > @@ -501,10 +504,12 @@ static int mlock_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > */ > > > if ((newflags & VM_LOCKED) && (oldflags & VM_LOCKED)) { > > > /* No work to do, and mlocking twice would be wrong */ > > > > I'd move this comment down to the vm_flags_reset() line as it's not applicable > > if we fail to get the lock. > > Ack. Thanks! > > > > > > > > - vma_start_write(vma); > > > + ret = vma_start_write_killable(vma); > > > + if (ret) > > > + goto out; > > > vm_flags_reset(vma, newflags); > > > } else { > > > - mlock_vma_pages_range(vma, start, end, newflags); > > > + ret = mlock_vma_pages_range(vma, start, end, newflags); > > > } > > > out: > > > *prev = vma; > > > @@ -733,9 +738,13 @@ static int apply_mlockall_flags(int flags) > > > > > > error = mlock_fixup(&vmi, vma, &prev, vma->vm_start, vma->vm_end, > > > newflags); > > > - /* Ignore errors, but prev needs fixing up. */ > > > - if (error) > > > + /* Ignore errors except EINTR, but prev needs fixing up. */ > > > > Well, except you're not fixing it up on -EINTR? This comment should be redone. > > Hmm, should we fixup if the process is terminating? Does it matter at > this point? We may as well keep the comment accurate though? I mean this isn't a big deal :) > > > > > But I wonder if this is correct? We are ignoring all other errors that > > interrupted the operation, so why are we special casing -EINTR? > > Well, -EINTR means all the work you are doing here is useless because > the process is about to go away. So, in that respect I think it's > different from other errors. Well -EINTR doesn't _just_ mean fatal signal. We happen to know here that what we're calling will only return -EINTR in that case, but if somebody changes downstream code to return -EINTR for _another_ reason there's an issue. Can we just replace these horrid -EINTR checks with is_fatal_signal_pending(current)? > > > > > > + if (error) { > > > + if (error == -EINTR) > > > + return error; > > > + > > > prev = vma; > > > + } > > > cond_resched(); > > > } > > > out: > > > diff --git a/mm/mprotect.c b/mm/mprotect.c > > > index c0571445bef7..49dbb7156936 100644 > > > --- a/mm/mprotect.c > > > +++ b/mm/mprotect.c > > > @@ -765,7 +765,9 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb, > > > * vm_flags and vm_page_prot are protected by the mmap_lock > > > * held in write mode. > > > */ > > > - vma_start_write(vma); > > > + error = vma_start_write_killable(vma); > > > + if (error < 0) > > > > Weird inconstency here, this should be if (error). > > Ack. Thanks! > > > > > > + goto fail; > > > vm_flags_reset_once(vma, newflags); > > > if (vma_wants_manual_pte_write_upgrade(vma)) > > > mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; > > > diff --git a/mm/mremap.c b/mm/mremap.c > > > index 2be876a70cc0..aef1e5f373c7 100644 > > > --- a/mm/mremap.c > > > +++ b/mm/mremap.c > > > @@ -1286,7 +1286,9 @@ static unsigned long move_vma(struct vma_remap_struct *vrm) > > > return -ENOMEM; > > > > > > /* We don't want racing faults. */ > > > - vma_start_write(vrm->vma); > > > + err = vma_start_write_killable(vrm->vma); > > > + if (err) > > > + return err; > > > > > > /* Perform copy step. */ > > > err = copy_vma_and_data(vrm, &new_vma); > > > diff --git a/mm/vma.c b/mm/vma.c > > > index bb4d0326fecb..9f2664f1d078 100644 > > > --- a/mm/vma.c > > > +++ b/mm/vma.c > > > @@ -530,6 +530,13 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > if (err) > > > goto out_free_vmi; > > > > > > + err = vma_start_write_killable(vma); > > > + if (err) > > > + goto out_free_mpol; > > > + err = vma_start_write_killable(new); > > > + if (err) > > > + goto out_free_mpol; > > > + > > > err = anon_vma_clone(new, vma, VMA_OP_SPLIT); > > > if (err) > > > goto out_free_mpol; > > > @@ -540,9 +547,6 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > if (new->vm_ops && new->vm_ops->open) > > > new->vm_ops->open(new); > > > > > > - vma_start_write(vma); > > > - vma_start_write(new); > > > - > > > > Again you're changing ordering seemingly arbitrarily. > > I moved it up to avoid undoing all the work above (vm_ops->open, > vma_dup_policy, vma_iter_prealloc, vm_area_dup,..) > > > I think this is actually a > > more problematic case as you're now invoking vm_ops->open() with a VMA write > > lock held. > > Are you concerned about potential increased duration of the vma lock > being held or that open() might try to take that lock itself (which is > not a problem because vma write locks are reentrant)? Maybe some other > concern I'm missing? General concern about reordering, but fair point re: undoing. rmap.c says it's ok so we're good: * vma_start_write * mapping->i_mmap_rwsem * anon_vma->rwsem > > > > > So I think you should keep the existing position. > > If we do that then we would have to undo a bunch of operations. I'm > fine adding that if there are reasons to avoid this move. OK fair enough in this case. > > > > > > init_vma_prep(&vp, vma); > > > vp.insert = new; > > > vma_prepare(&vp); > > > @@ -895,16 +899,22 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( > > > } > > > > > > /* No matter what happens, we will be adjusting middle. */ > > > - vma_start_write(middle); > > > + err = vma_start_write_killable(middle); > > > + if (err) > > > + goto abort; > > > > > > if (merge_right) { > > > - vma_start_write(next); > > > + err = vma_start_write_killable(next); > > > + if (err) > > > + goto abort; > > > vmg->target = next; > > > sticky_flags |= (next->vm_flags & VM_STICKY); > > > } > > > > > > if (merge_left) { > > > - vma_start_write(prev); > > > + err = vma_start_write_killable(prev); > > > + if (err) > > > + goto abort; > > > vmg->target = prev; > > > sticky_flags |= (prev->vm_flags & VM_STICKY); > > > } > > > @@ -1155,10 +1165,12 @@ int vma_expand(struct vma_merge_struct *vmg) > > > struct vm_area_struct *next = vmg->next; > > > bool remove_next = false; > > > vm_flags_t sticky_flags; > > > - int ret = 0; > > > + int ret; > > > > > > mmap_assert_write_locked(vmg->mm); > > > - vma_start_write(target); > > > + ret = vma_start_write_killable(target); > > > + if (ret) > > > + return ret; > > > > > > if (next && target != next && vmg->end == next->vm_end) > > > remove_next = true; > > > @@ -1187,6 +1199,9 @@ int vma_expand(struct vma_merge_struct *vmg) > > > * we don't need to account for vmg->give_up_on_mm here. > > > */ > > > if (remove_next) { > > > + ret = vma_start_write_killable(next); > > > + if (ret) > > > + return ret; > > > ret = dup_anon_vma(target, next, &anon_dup); > > > if (ret) > > > return ret; > > > @@ -1197,10 +1212,8 @@ int vma_expand(struct vma_merge_struct *vmg) > > > return ret; > > > } > > > > > > - if (remove_next) { > > > - vma_start_write(next); > > > + if (remove_next) > > > vmg->__remove_next = true; > > > - } > > > > Hmm you're moving the ordering of things around again :) You should have made > > this change as part of patch 1 anyway first so this patch wouldn't have a > > refactoring in it too. > > > > Top of rmap.c suggests you _can_ take the VMA write lock prior to trying the dup > > but I'm just not sure why you'd want to switch these around in this patch? > > > > Can we try to keep original ordering unless there's a really good reason not to? > > Again, I'm trying to avoid undoing things if locking fails but this > function already has rollback code, so I can reuse it. I'll keep the > old placement here. Ack yeah... :) We're safe with vma -> anon rmap lock anyway. > > > > > > if (commit_merge(vmg)) > > > goto nomem; > > > > > > @@ -1233,6 +1246,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > unsigned long start, unsigned long end, pgoff_t pgoff) > > > { > > > struct vma_prepare vp; > > > + int err; > > > > > > WARN_ON((vma->vm_start != start) && (vma->vm_end != end)); > > > > > > @@ -1244,7 +1258,11 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > if (vma_iter_prealloc(vmi, NULL)) > > > return -ENOMEM; > > > > > > - vma_start_write(vma); > > > + err = vma_start_write_killable(vma); > > > + if (err) { > > > + vma_iter_free(vmi); > > > + return err; > > > + } > > > > > > init_vma_prep(&vp, vma); > > > vma_prepare(&vp); > > > @@ -1434,7 +1452,9 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, > > > if (error) > > > goto end_split_failed; > > > } > > > - vma_start_write(next); > > > + error = vma_start_write_killable(next); > > > + if (error) > > > + goto munmap_gather_failed; > > > mas_set(mas_detach, vms->vma_count++); > > > error = mas_store_gfp(mas_detach, next, GFP_KERNEL); > > > if (error) > > > @@ -1828,12 +1848,17 @@ static void vma_link_file(struct vm_area_struct *vma, bool hold_rmap_lock) > > > static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > > > { > > > VMA_ITERATOR(vmi, mm, 0); > > > + int err; > > > > > > vma_iter_config(&vmi, vma->vm_start, vma->vm_end); > > > if (vma_iter_prealloc(&vmi, vma)) > > > return -ENOMEM; > > > > > > - vma_start_write(vma); > > > + err = vma_start_write_killable(vma); > > > + if (err) { > > > + vma_iter_free(&vmi); > > > + return err; > > > + } > > > vma_iter_store_new(&vmi, vma); > > > vma_link_file(vma, /* hold_rmap_lock= */false); > > > mm->map_count++; > > > @@ -2215,9 +2240,8 @@ int mm_take_all_locks(struct mm_struct *mm) > > > * is reached. > > > */ > > > for_each_vma(vmi, vma) { > > > - if (signal_pending(current)) > > > + if (signal_pending(current) || vma_start_write_killable(vma)) > > > goto out_unlock; > > > - vma_start_write(vma); > > > } > > > > > > vma_iter_init(&vmi, mm, 0); > > > @@ -2522,6 +2546,11 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap) > > > if (!vma) > > > return -ENOMEM; > > > > > > + /* Lock the VMA since it is modified after insertion into VMA tree */ > > > + error = vma_start_write_killable(vma); > > > + if (error) > > > + goto free_vma; > > > + > > > > You're doing it again :) > > > > Can we please keep the lock acquisition at the point it is in unless there's a > > really good reason not to. > > > > And if there is a good reason, please do it in another commit prior to the > > massive 'change everything' one so it's more easily reviewable :) > > The reason for this one is that I want to avoid undoing > __mmap_new_file_vma() if we fail to lock the VMA later. Undoing that > one would be messy, so I would prefer locking it earlier. These > operations are already performed under the mmap write lock. Is that > really a problem if we write-lock the VMA as well? This is a fair point, I obviously glanced over this without thinking about that :) I think you should include in the commit message why you're reordering though. > > > > > > vma_iter_config(vmi, map->addr, map->end); > > > vma_set_range(vma, map->addr, map->end, map->pgoff); > > > vm_flags_init(vma, map->vm_flags); > > > @@ -2552,8 +2581,6 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap) > > > WARN_ON_ONCE(!arch_validate_flags(map->vm_flags)); > > > #endif > > > > > > - /* Lock the VMA since it is modified after insertion into VMA tree */ > > > - vma_start_write(vma); > > > vma_iter_store_new(vmi, vma); > > > map->mm->map_count++; > > > vma_link_file(vma, map->hold_file_rmap_lock); > > > @@ -2864,6 +2891,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > unsigned long addr, unsigned long len, vm_flags_t vm_flags) > > > { > > > struct mm_struct *mm = current->mm; > > > + int err = -ENOMEM; > > > > I hate this 'default error code' pattern, it's a code smell. Please update > > everything that jumps to the failure case to set err, and leave this > > uninitialised. > > > > We've had real bugs come out of this before! > > Ack. Thanks! > > > > > > > > > /* > > > * Check against address space limits by the changed size > > > @@ -2908,7 +2936,10 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > vma_set_range(vma, addr, addr + len, addr >> PAGE_SHIFT); > > > vm_flags_init(vma, vm_flags); > > > vma->vm_page_prot = vm_get_page_prot(vm_flags); > > > - vma_start_write(vma); > > > + if (vma_start_write_killable(vma)) { > > > + err = -EINTR; > > > + goto mas_store_fail; > > > + } > > > if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL)) > > > goto mas_store_fail; > > > > > > @@ -2928,7 +2959,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > vm_area_free(vma); > > > unacct_fail: > > > vm_unacct_memory(len >> PAGE_SHIFT); > > > - return -ENOMEM; > > > + return err; > > > } > > > > > > /** > > > @@ -3089,7 +3120,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) > > > struct mm_struct *mm = vma->vm_mm; > > > struct vm_area_struct *next; > > > unsigned long gap_addr; > > > - int error = 0; > > > + int error; > > > VMA_ITERATOR(vmi, mm, vma->vm_start); > > > > > > if (!(vma->vm_flags & VM_GROWSUP)) > > > @@ -3126,12 +3157,14 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) > > > > > > /* We must make sure the anon_vma is allocated. */ > > > if (unlikely(anon_vma_prepare(vma))) { > > > - vma_iter_free(&vmi); > > > - return -ENOMEM; > > > + error = -ENOMEM; > > > + goto free; > > > } > > > > > > /* Lock the VMA before expanding to prevent concurrent page faults */ > > > - vma_start_write(vma); > > > + error = vma_start_write_killable(vma); > > > + if (error) > > > + goto free; > > > /* We update the anon VMA tree. */ > > > anon_vma_lock_write(vma->anon_vma); > > > > > > @@ -3160,6 +3193,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) > > > } > > > } > > > anon_vma_unlock_write(vma->anon_vma); > > > +free: > > > > Nitty, but this kinda sucks as a label name, generally when the error label > > contains 'free' it is free_xxx where 'xxx' is some specific thing. > > > > So somethiing like 'fail' would be good. > > Ack. Will change to something more appropriate. Thanks! > > > > > > vma_iter_free(&vmi); > > > validate_mm(mm); > > > return error; > > > @@ -3174,7 +3208,7 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address) > > > { > > > struct mm_struct *mm = vma->vm_mm; > > > struct vm_area_struct *prev; > > > - int error = 0; > > > + int error; > > > VMA_ITERATOR(vmi, mm, vma->vm_start); > > > > > > if (!(vma->vm_flags & VM_GROWSDOWN)) > > > @@ -3205,12 +3239,14 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address) > > > > > > /* We must make sure the anon_vma is allocated. */ > > > if (unlikely(anon_vma_prepare(vma))) { > > > - vma_iter_free(&vmi); > > > - return -ENOMEM; > > > + error = -ENOMEM; > > > + goto free; > > > } > > > > > > /* Lock the VMA before expanding to prevent concurrent page faults */ > > > - vma_start_write(vma); > > > + error = vma_start_write_killable(vma); > > > + if (error) > > > + goto free; > > > /* We update the anon VMA tree. */ > > > anon_vma_lock_write(vma->anon_vma); > > > > > > @@ -3240,6 +3276,7 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address) > > > } > > > } > > > anon_vma_unlock_write(vma->anon_vma); > > > +free: > > > > Obviously same comment her :) > > Ack. Thanks! > > > > > > vma_iter_free(&vmi); > > > validate_mm(mm); > > > return error; > > > diff --git a/mm/vma_exec.c b/mm/vma_exec.c > > > index 8134e1afca68..a4addc2a8480 100644 > > > --- a/mm/vma_exec.c > > > +++ b/mm/vma_exec.c > > > @@ -40,6 +40,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift) > > > struct vm_area_struct *next; > > > struct mmu_gather tlb; > > > PAGETABLE_MOVE(pmc, vma, vma, old_start, new_start, length); > > > + int err; > > > > > > BUG_ON(new_start > new_end); > > > > > > @@ -55,8 +56,9 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift) > > > * cover the whole range: [new_start, old_end) > > > */ > > > vmg.target = vma; > > > - if (vma_expand(&vmg)) > > > - return -ENOMEM; > > > + err = vma_expand(&vmg); > > > + if (err) > > > + return err; > > > > Hmm. But before we were filtering the errors and now we're not... I guess not an > > issue as before it could _only_ return -ENOMEM, but again, are we sure all > > callers are fine with -EINTR I guess :) > > This function is called only from setup_arg_pages() and all its > callers end up being linux_binfmt.load_binary handlers. The returned > error propagates all the way to execve() and its friends. And with my > extreme "luck" the execve syscall lists probably every single possible > error code except EINTR :) This is depressing... Well as per Matthew's point this is probably fine. > > Thanks for the detailed review, Lorenzo! I guess we need to discuss > these lock moves a bit more before I start on the new version. Nah I think we're good after this! > > > > > > > > > /* > > > * move the page tables downwards, on failure we rely on > > > -- > > > 2.53.0.414.gf7e9f6c205-goog > > > > > > > Cheers, Lorenzo > > Cheers, Lorenzo