On Fri, Aug 16, 2019 at 05:19:38PM -0500, Eric W. Biederman wrote:
My recent to change to only use force_sig for a synchronous events wound up breaking signal reception cifs and drbd. I had overlooked the fact that by default kthreads start out with all signals set to SIG_IGN. So a change I thought was safe turned out to have made it impossible for those kernel thread to catch their signals.
Reverting the work on force_sig is a bad idea because what the code was doing was very much a misuse of force_sig. As the way force_sig ultimately allowed the signal to happen was to change the signal handler to SIG_DFL. Which after the first signal will allow userspace to send signals to these kernel threads. At least for wake_ack_receiver in drbd that does not appear actively wrong.
So correct this problem by adding allow_kernel_signal that will allow signals whose siginfo reports they were sent by the kernel through, but will not allow userspace generated signals, and update cifs and drbd to call allow_kernel_signal in an appropriate place so that their thread can receive this signal.
Fixing things this way ensures that userspace won't be able to send signals and cause problems, that it is clear which signals the threads are expecting to receive, and it guarantees that nothing else in the system will be affected.
This change was partly inspired by similar cifs and drbd patches that added allow_signal.
Reported-by: ronnie sahlberg ronniesahlberg@gmail.com Reported-by: Christoph Böhmwalder christoph.boehmwalder@linbit.com Cc: Steve French smfrench@gmail.com Cc: Philipp Reisner philipp.reisner@linbit.com Cc: David Laight David.Laight@ACULAB.COM Fixes: 247bc9470b1e ("cifs: fix rmmod regression in cifs.ko caused by force_sig changes") Fixes: 72abe3bcf091 ("signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig") Fixes: fee109901f39 ("signal/drbd: Use send_sig not force_sig") Fixes: 3cf5d076fb4d ("signal: Remove task parameter from force_sig") Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com
drivers/block/drbd/drbd_main.c | 2 ++ fs/cifs/connect.c | 2 +- include/linux/signal.h | 15 ++++++++++++++- kernel/signal.c | 5 +++++ 4 files changed, 22 insertions(+), 2 deletions(-)
Just tested this patch, and I can confirm that it makes DRBD work as intended again.
Tested-by: Christoph Böhmwalder christoph.boehmwalder@linbit.com
-- Christoph Böhmwalder LINBIT | Keeping the Digital World Running DRBD HA — Disaster Recovery — Software defined Storage