Date: Mon, 2 Oct 2023 11:50:46 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: e61568aeeec7 - main - swap_pager: Fix a race in swap_pager_swapoff_object() Message-ID: <202310021150.392BokhA028387@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=e61568aeeec7667789e6c9d4837e074edecc990e commit e61568aeeec7667789e6c9d4837e074edecc990e Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2023-10-02 11:49:27 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2023-10-02 11:49:52 +0000 swap_pager: Fix a race in swap_pager_swapoff_object() When we disable swapping to a device, we scan the full VM object list looking for objects with swap trie nodes that reference the device in question. The pages corresponding to those nodes are paged in. While paging in, we drop the VM object lock. Moreover, we do not hold a reference for the object; swap_pager_swapoff_object() merely bumps the paging-in-progress counter. vm_object_terminate() waits for this counter to drain before proceeding and freeing pages. However, swap_pager_swapoff_object() decrements the counter before re-acquiring the VM object lock, which means that vm_object_terminate() can race to acquire the lock and free the pages. Then, swap_pager_swapoff_object() ends up unbusying a freed page. Fix the problem by acquiring the lock before waking up sleepers. PR: 273610 Reported by: Graham Perrin <grahamperrin@gmail.com> Reviewed by: kib MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D42029 --- sys/vm/swap_pager.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c index e548c2d16a0b..38151b3be96f 100644 --- a/sys/vm/swap_pager.c +++ b/sys/vm/swap_pager.c @@ -1890,8 +1890,8 @@ swap_pager_swapoff_object(struct swdevt *sp, vm_object_t object) if (rv != VM_PAGER_OK) panic("%s: read from swap failed: %d", __func__, rv); - vm_object_pip_wakeupn(object, 1); VM_OBJECT_WLOCK(object); + vm_object_pip_wakeupn(object, 1); vm_page_xunbusy(m); /*
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