From c78fe96446794f71a2db7d7e3d43cb15658590a3 Mon Sep 17 00:00:00 2001 From: Richard Braun Date: Fri, 16 Sep 2016 04:39:02 +0200 Subject: VM: improve pageout deadlock workaround Commit 5dd4f67522ad0d49a2cecdb9b109251f546d4dd1 makes VM map entry allocation done with VM privilege, so that a VM map isn't held locked while physical allocations are paused, which may block the default pager during page eviction, causing a system-wide deadlock. First, it turns out that map entries aren't the only buffers allocated, and second, their number can't be easily determined, which makes a preallocation strategy very hard to implement. This change generalizes the strategy of VM privilege increase when a VM map is locked. * device/ds_routines.c (io_done_thread): Use integer values instead of booleans when setting VM privilege. * kern/thread.c (thread_init, thread_wire): Likewise. * vm/vm_pageout.c (vm_pageout): Likewise. * kern/thread.h (struct thread): Turn member `vm_privilege' into an unsigned integer. * vm/vm_map.c (vm_map_lock): New function, where VM privilege is temporarily increased. (vm_map_unlock): New function, where VM privilege is decreased. (_vm_map_entry_create): Remove VM privilege workaround from this function. * vm/vm_map.h (vm_map_lock, vm_map_unlock): Turn into functions. --- kern/thread.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'kern/thread.h') diff --git a/kern/thread.h b/kern/thread.h index 7106fd2d..f0ed71a8 100644 --- a/kern/thread.h +++ b/kern/thread.h @@ -77,7 +77,6 @@ struct thread { struct { unsigned state:16; unsigned wake_active:1; - unsigned vm_privilege:1; unsigned active:1; }; event_t event_key; @@ -146,8 +145,8 @@ struct thread { /* VM global variables */ vm_offset_t recover; /* page fault recovery (copyin/out) */ - /* Defined above */ - /* boolean_t vm_privilege; Can use reserved memory? */ + unsigned int vm_privilege; /* Can use reserved memory? + Implemented as a counter */ /* User-visible scheduling state */ int user_stop_count; /* outstanding stops */ -- cgit v1.2.3