Messages in this thread | | | Date | Wed, 17 Jan 2018 19:04:50 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2 1/3] Revert "do_SAK: Don't recursively take the tasklist_lock" |
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On 01/17, Eric W. Biederman wrote: > > Oleg Nesterov <oleg@redhat.com> writes: > > > On 01/17, Eric W. Biederman wrote: > > > >> Kirill Tkhai <ktkhai@virtuozzo.com> writes: > >> > >> > This reverts commit 20ac94378de5. > >> > > >> > send_sig() does not take tasklist_lock for a long time, > >> > so this commit and the problem it solves are not relevant > >> > anymore. > >> > > >> > Also, the problem of force_sig() is it clears SIGNAL_UNKILLABLE > >> > flag, thus even global init may be killed by __do_SAK(), > >> > which is definitely not the expected behavior. > >> > >> Actually it is. > >> > >> SAK should kill everything that has the tty open. If init opens the tty > >> I am so sorry, it can not operate correctly. init should not have your > >> tty open. > > > > OK, but then we need "force" in other places too. __do_SAK() does send_sig(SIGKILL) > > in do_each_pid_task(PIDTYPE_SID) and if signal->tty == tty. > > > > Plus force_sig() is not rcu-friendly. > > > > So I personally agree with this change. Whether we want to kill the global init > > or not should be discussed, if we want to do this __do_SAK() should use > > SEND_SIG_FORCED and this is what Kirill is going to do (iiuc), but this needs > > another patch. > > To operate correctly, do_SAK() needs to kill everything that has the tty > open. Unless we can make that guarantee I don't see the point of > changing do_SAK.
OK, but how this connects to this change?
Again, this force_sig() doesn't match other send_sig()'s in __do_SAK(), and Kirill is going to turn them all into send_sig_info(SEND_SIG_FORCED). Just we need to discuss whether we need to skip the global init or not but this is another story.
So why do you dislike this change?
force_sig() should die anyway. At least in its current form, it should not be used unless task == current. But this is off-topic.
Oleg.
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