El Sat, 27 Mar 2010 00:39:19 +0100 Samuel Thibault <samuel.thiba...@gnu.org> escribió:
> Hello, > > From times to times, ext2fs deadlocks on the pager->interlock mutex. > This is an excerpt of what I could find in the process: > > #2 0x08106e59 in memory_object_lock_request () > #3 0x0806fdeb in _pager_lock_object (p=0x81c97b8, offset=0, > size=827392, should_return=2, should_flush=0, lock_value=8, sync=0) > at /var/tmp/hurd-20090404/./libpager/lock-object.c:68 #4 0x0806da18 > in pager_sync (p=0x81c97b8, wait=0) > at /var/tmp/hurd-20090404/./libpager/pager-sync.c:31 ... #9 > 0x0805a9ac in periodic_sync (interval=5) > at /var/tmp/hurd-20090404/./libdiskfs/sync-interval.c:119 > > This is the periodic sync, calling memory_object_lock_request() on the > pager. Note that before doing this, _pager_lock_object takes > pager->interlock. > AFAIK, m_o_lock_request is an asynchronous operation, so it should not block in any case. Perhaps the cthreads package is behaving weird? > #3 0x08079662 in __mutex_lock_solid (ptr=0x81c97f0) > at /var/tmp/hurd-20090404/./libthreads/cprocs.c:955 #4 0x0806f7ff in > _pager_do_write_request (object=1305, seqno=413, control=1819, > offset=618496, data=6467584, length=98304, dirty=1, kcopy=1, > initializing=0) > at /var/tmp/hurd-20090404/./libpager/data-return.c:174 #5 0x0806f88a > in _pager_seqnos_memory_object_data_return (object=1305, seqno=413, > control=1819, offset=618496, data=6467584, length=98304, dirty=1, > kcopy=1) at /var/tmp/hurd-20090404/./libpager/data-return.c:272 #6 > 0x0806e65e in _Xmemory_object_data_return (InHeadP=0x1, > OutHeadP=0x10fbf40) at memory_objectServer.c:837 > > This is a memory_object_data_return() call from the kernel, trying to > take the pager->interlock mutex, but waiting for the periodic sync > thread to free it. > > I don't have the gdb under the hand any more so can't check it for > sure, but I do see in GNU Mach's source that > memory_object_lock_request() may make memory_object_data_return() > calls on the objects of the pager to be synced. Since these calls > will need to take the interlock mutex as the trace above shows, this > can not be but potentially deadlock. Am I missing something? > > I haven't found any documentation about what interlock is exactly > supposed to protect, so I can't really decide what to do here, I guess > just releasing around the memory_object_lock_request() call is not > safe for instance. Any thoughts? > > It is worth noting that by default, the kernel does not call > memory_object_data_return because by default use_old_pageout is > TRUE. But as soon as pager_change_attributes() (thus Mach's > memory_object_change_attributes()) is called, it turns to FALSE. One > way to trigger it is to just call truncate() on a file, thus calling > ext2fs_truncate() which ends up calling pager_change_attributes at > some point. > > Samuel > > > >
