CVSROOT: /cvs
Module name: src
Changes by: an...@cvs.openbsd.org 2020/10/26 13:48:19
Modified files:
sys/uvm : uvm_vnode.c uvm_vnode.h
Log message:
Fix a deadlock between uvn_io() and uvn_flush(). While faulting on a
page backed by a vnode, uvn_io() will end up being called in order to
populate newly allocated pages using I/O on the backing vnode. Before
performing the I/O, newly allocated pages are flagged as busy by
uvn_get(), that is before uvn_io() tries to lock the vnode. Such pages
could then end up being flushed by uvn_flush() which already has
acquired the vnode lock. Since such pages are flagged as busy,
uvn_flush() will wait for them to be flagged as not busy. This will
never happens as uvn_io() cannot make progress until the vnode lock is
released.
Instead, grab the vnode lock before allocating and flagging pages as
busy in uvn_get(). This does extend the scope in uvn_get() in which the
vnode is locked but resolves the deadlock.
ok mpi@
Reported-by: syzbot+e63407b35dff08dbe...@syzkaller.appspotmail.com
