Ensure round-robin works properly List-Id: Commit messages for all branches of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-all List-Help: List-Post: List-Subscribe: List-Unsubscribe: X-BeenThere: dev-commits-src-all@freebsd.org Sender: owner-dev-commits-src-all@FreeBSD.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: olce X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 7b0fe2d405ae09b1247bccc6fa45a6d2755cbe4c Auto-Submitted: auto-generated The branch main has been updated by olce: URL: https://cgit.FreeBSD.org/src/commit/?id=7b0fe2d405ae09b1247bccc6fa45a6d2755cbe4c commit 7b0fe2d405ae09b1247bccc6fa45a6d2755cbe4c Author: Olivier Certner AuthorDate: 2025-09-25 14:40:30 +0000 Commit: Olivier Certner CommitDate: 2025-10-17 15:18:53 +0000 vm_domainset: Ensure round-robin works properly All iterators that rely on an object's 'struct domainset_ref' (field 'domain' on 'struct vm_object'), which is the case for page allocations with objects, are used with the corresponding object locked for writing, so cannot lose concurrent iterator index's increases even if those are made without atomic operations. The only offender was thread stack allocation, which has just been fixed in commit 3b9b64457676 ("vm: Fix iterator usage in vm_thread_stack_create()"). However, the interleaved policy would still reset the iterator index when restarting, losing track of the next domain to allocate from when applying round-robin, which all allocation policies do if allocation from the first domain fails. Fix this last round-robin problem by not resetting the shared index at iterator's phase init on DOMAINSET_POLICY_INTERLEAVE. Add an assertion to check that, when passed, an object is write-locked in order to prevent the problem mentioned in the first paragraph from reappearing. Reviewed by: markj MFC after: 1 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D52733 --- sys/vm/vm_domainset.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/sys/vm/vm_domainset.c b/sys/vm/vm_domainset.c index 9fa17da954f7..c25ed0cc2267 100644 --- a/sys/vm/vm_domainset.c +++ b/sys/vm/vm_domainset.c @@ -113,7 +113,6 @@ vm_domainset_iter_interleave(struct vm_domainset_iter *di, int *domain) int d; d = di->di_offset % di->di_domain->ds_cnt; - *di->di_iter = d; *domain = di->di_domain->ds_order[d]; } @@ -260,9 +259,14 @@ vm_domainset_iter_page_init(struct vm_domainset_iter *di, struct vm_object *obj, * are immutable and unsynchronized. Updates can race but pointer * loads are assumed to be atomic. */ - if (obj != NULL && obj->domain.dr_policy != NULL) + if (obj != NULL && obj->domain.dr_policy != NULL) { + /* + * This write lock protects non-atomic increments of the + * iterator index in vm_domainset_iter_rr(). + */ + VM_OBJECT_ASSERT_WLOCKED(obj); dr = &obj->domain; - else + } else dr = &curthread->td_domain; vm_domainset_iter_init(di, dr->dr_policy, &dr->dr_iter, obj, pindex);