I'm observing a crash when a utility driver is disabled host side (e.g. 'Guest services' is disabled live) when we have userspace daemon connected:
[ 90.244859] general protection fault: 0000 [#1] SMP ... [ 90.800082] CPU: 3 PID: 473 Comm: hypervfcopyd Not tainted 4.3.0-rc7_netvsc_noalloc+ #1053 ... [ 90.800082] Call Trace: [ 90.800082] [<ffffffff81187008>] __fput+0xc8/0x1f0 [ 90.800082] [<ffffffff8118716e>] ____fput+0xe/0x10 [ 90.800082] [<ffffffff8107e4b3>] task_work_run+0x73/0x90 [ 90.800082] [<ffffffff81066995>] do_exit+0x335/0xa90 [ 90.800082] [<ffffffff8106716f>] do_group_exit+0x3f/0xc0 [ 90.800082] [<ffffffff81071abe>] get_signal+0x25e/0x5e0 [ 90.800082] [<ffffffff81015278>] do_signal+0x28/0x580 [ 90.800082] [<ffffffff81086656>] ? finish_task_switch+0xa6/0x180 [ 90.800082] [<ffffffff81443ebf>] ? __schedule+0x28f/0x870 [ 90.800082] [<ffffffffa01ebbaa>] ? hvt_op_read+0x12a/0x140 [hv_utils] [ 90.800082] [<ffffffff8109eca0>] ? wake_atomic_t_function+0x70/0x70 ... [ 90.800082] RIP [<ffffffff810d3866>] module_put+0x16/0x90 [ 90.800082] RSP <ffff88003eb1bb88> [ 95.734261] ---[ end trace 0e09af6a6294a668 ]--- The problem is that hvutil_transport_destroy() which does misc_deregister() freeing the appropriate device is reachable by two paths: module unload and from util_remove(). While module unload path is protected by .owner in struct file_operations util_remove() path is not. Freeing the device while someone holds an open fd for it is a show stopper. In general, it is not possible to revoke an fd from all users so the only way to solve the issue is to defer freeing the hvutil_transport structure asking the daemon to exit gracefully by responding -EBADF to all operations on unload. Patch 1 fixes an unrelated issue I spotted, patch 2 renames outmsg_lock to 'lock' as we're gonna use it to protect test-and-set operations on 'mode', patch 3 introduces HVUTIL_TRANSPORT_DESTROY mode of operation, patch 4 fixes the issue itself. Patches are rebased on previously sent Olaf's fixes. Vitaly Kuznetsov (4): Drivers: hv: utils: fix memory leak on on_msg() failure Drivers: hv: utils: rename outmsg_lock Drivers: hv: utils: introduce HVUTIL_TRANSPORT_DESTROY mode Drivers: hv: utils: fix crash when device is removed from host side drivers/hv/hv_utils_transport.c | 110 +++++++++++++++++++++++++++++++--------- drivers/hv/hv_utils_transport.h | 3 +- 2 files changed, 88 insertions(+), 25 deletions(-) -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
