Date: Sun, 14 Sep 2025 20:13:24 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: a38483fa2b3a - main - vm_fault: assert that first_m is xbusy Message-ID: <202509142013.58EKDOob066163@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=a38483fa2b3a26414d3409b12dd35ac406c44cea commit a38483fa2b3a26414d3409b12dd35ac406c44cea Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2025-08-05 15:46:56 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2025-09-14 20:00:36 +0000 vm_fault: assert that first_m is xbusy There are several invariants, most important of which is prevention of parallel faults handling, that depend on first_m being xbusy for the duration of the page fault processing. Suggested by: markj Reviewed by: alc, markj Tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D51474 --- sys/vm/vm_fault.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c index 427c18c63eb7..3dddc7a307d4 100644 --- a/sys/vm/vm_fault.c +++ b/sys/vm/vm_fault.c @@ -1784,6 +1784,11 @@ found: /* * A valid page has been found and busied. The object lock * must no longer be held if the page was busied. + * + * Regardless of the busy state of fs.m, fs.first_m is always + * exclusively busied after the first iteration of the loop + * calling vm_fault_object(). This is an ordering point for + * the parallel faults occuring in on the same page. */ vm_page_assert_busied(fs.m); VM_OBJECT_ASSERT_UNLOCKED(fs.object); @@ -1886,6 +1891,9 @@ found: (*fs.m_hold) = fs.m; vm_page_wire(fs.m); } + + KASSERT(fs.first_object == fs.object || vm_page_xbusied(fs.first_m), + ("first_m must be xbusy")); if (vm_page_xbusied(fs.m)) vm_page_xunbusy(fs.m); else
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