From a8a5d270ff8e63f9fccf74118714bb29dee68b16 Mon Sep 17 00:00:00 2001 From: mpi Date: Thu, 7 Jul 2022 13:52:20 +0000 Subject: [PATCH] Revert previous attempt at serializing `uo_refs'. It is incorrect to look at/modify `uo_refs' without lock in uvm_vnp_sync(). However sleeping is not possible and spinning introduces a deadlock with the KERNEL_LOCK() when another thread faults on a mmaped region related to a vnode we're currently synching. A proper fix should be investigated. For now a kown a race, mostly safe due to the KERNEL_LOCK(), is better than a possible deadlock. Issue reported by caspar@ Discussed with and ok semarie@ --- sys/uvm/uvm_vnode.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) diff --git a/sys/uvm/uvm_vnode.c b/sys/uvm/uvm_vnode.c index 8824d62a356..b35e864670c 100644 --- a/sys/uvm/uvm_vnode.c +++ b/sys/uvm/uvm_vnode.c @@ -1,4 +1,4 @@ -/* $OpenBSD: uvm_vnode.c,v 1.124 2022/05/03 21:20:35 bluhm Exp $ */ +/* $OpenBSD: uvm_vnode.c,v 1.125 2022/07/07 13:52:20 mpi Exp $ */ /* $NetBSD: uvm_vnode.c,v 1.36 2000/11/24 20:34:01 chs Exp $ */ /* @@ -1472,11 +1472,6 @@ uvm_vnp_sync(struct mount *mp) if (mp && vp->v_mount != mp) continue; - /* Spin to ensure `uvn_wlist' isn't modified concurrently. */ - while (rw_enter(uvn->u_obj.vmobjlock, RW_WRITE|RW_NOSLEEP)) { - CPU_BUSY_CYCLE(); - } - /* * If the vnode is "blocked" it means it must be dying, which * in turn means its in the process of being flushed out so @@ -1485,10 +1480,8 @@ uvm_vnp_sync(struct mount *mp) * note that uvn must already be valid because we found it on * the wlist (this also means it can't be ALOCK'd). */ - if ((uvn->u_flags & UVM_VNODE_BLOCKED) != 0) { - rw_exit(uvn->u_obj.vmobjlock); + if ((uvn->u_flags & UVM_VNODE_BLOCKED) != 0) continue; - } /* * gain reference. watch out for persisting uvns (need to @@ -1497,7 +1490,6 @@ uvm_vnp_sync(struct mount *mp) if (uvn->u_obj.uo_refs == 0) vref(vp); uvn->u_obj.uo_refs++; - rw_exit(uvn->u_obj.vmobjlock); SIMPLEQ_INSERT_HEAD(&uvn_sync_q, uvn, u_syncq); } -- 2.20.1