From: ebiederm@xmission.com (Eric W. Biederman)
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Wen Yang <wen.yang99@zte.com.cn>,
majiang <ma.jiang@zte.com.cn>
Subject: Re: [PATCH 18/20] signal: Add calculate_sigpending()
Date: Thu, 26 Jul 2018 10:13:12 -0500 [thread overview]
Message-ID: <87tvom58tz.fsf@xmission.com> (raw)
In-Reply-To: <20180726132050.GA32718@redhat.com> (Oleg Nesterov's message of "Thu, 26 Jul 2018 15:20:50 +0200")
Oleg Nesterov <oleg@redhat.com> writes:
> On 07/23, Eric W. Biederman wrote:
>>
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -1988,6 +1988,7 @@ static __latent_entropy struct task_struct *copy_process(
>> &p->signal->thread_head);
>> }
>> attach_pid(p, PIDTYPE_PID);
>> + calculate_sigpending(p);
>
> In theory this looks racy if !CLONE_SIGHAND, please see below
>
>> +void calculate_sigpending(struct task_struct *new)
>> +{
>> + /* Have any signals or users of TIF_SIGPENDING been delayed
>> + * until after fork?
>> + */
>> + bool pending = (new->jobctl & JOBCTL_PENDING_MASK) ||
>> + PENDING(&new->pending, &new->blocked) ||
>> + PENDING(&new->signal->shared_pending, &new->blocked) ||
>> + freezing(new) || klp_patch_pending(new);
>
> note that we do not hold new->sighand->siglock, but this "new" task is already
> visible to find_task_by_vpid/etc; so a new signal can come right after
> this check,
Good point. The localtion of the call to calculate_sigpending is wrong.
>> + update_tsk_thread_flag(new, TIF_SIGPENDING, pending);
>
> and then update_tsk_thread_flag() can wrongly clear TIF_SIGPENDING.
>
> Easy to fix, but perhaps we can simply add recalc_sigpending() into
> schedule_tail() ? It already does more than just finish_task_switch/etc.
>
> This way we do not need the new helper (which btw can only be used by
> copy_process).
The problem I have with reusing recalc_sigpending is that it does not
set TIF_SIGPENDING if (freezing || klp_patch_pending).
There is obviously synergy between these two cases, I just have not
figured out how to take advantage of it yet.
> Note also that either way you can remove set_tsk_thread_flag(TIF_SIGPENDING)
> from ptrace_init_task().
Interesting. Yes we can remove TIF_SIGPENDING from that case because
ptrace_init_task sets jobctl or queues a pending signal. I like
that synergy. I like not being able to miss setting TIF_SIGPENDING
during fork.
Eric
next prev parent reply other threads:[~2018-07-26 15:13 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-200447-5873-b2kAsSyE1X@https.bugzilla.kernel.org/>
[not found] ` <CA+55aFyOaEGc_wjRuAxYZH7D4zi4xUQTqUwMmUzxFJQ__2pXuQ@mail.gmail.com>
[not found] ` <87h8l9p7bg.fsf@xmission.com>
[not found] ` <20180709104158.GA23796@redhat.com>
[not found] ` <87sh4so5jv.fsf@xmission.com>
[not found] ` <20180709145726.GA26149@redhat.com>
[not found] ` <877em4nxo0.fsf@xmission.com>
[not found] ` <CA+55aFwq90_KeRUesktap7L_4Hp3gatKZ28RYw1jXBYeOqUoeA@mail.gmail.com>
[not found] ` <87lgakm4ol.fsf@xmission.com>
[not found] ` <CA+55aFz1XFvOgJySKVNQD9VS4hys0J7rozxqd3s5ND0z80tfVw@mail.gmail.com>
[not found] ` <20180710134639.GA2453@redhat.com>
2018-07-10 16:00 ` [Bug 200447] infinite loop in fork syscall Eric W. Biederman
2018-07-11 12:08 ` Oleg Nesterov
[not found] ` <CA+55aFxcjSYAj-CZFEuDwiwZyMg+prV_jeP_Vuh06RJA0BboSw@mail.gmail.com>
2018-07-11 2:41 ` [RFC][PATCH 0/11] PIDTYPE_TGID and fewer fork restarts Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 01/11] pids: Initialize leader_pid in init_task Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 02/11] pids: Move task_pid_type into sched/signal.h Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 03/11] pids: Compute task_tgid using signal->leader_pid Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 04/11] kvm: Don't open code task_pid in kvm_vcpu_ioctl Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 05/11] pids: Move the pgrp and session pid pointers from task_struct to signal_struct Eric W. Biederman
2018-07-17 11:59 ` Oleg Nesterov
2018-07-11 2:44 ` [RFC][PATCH 06/11] pid: Implement PIDTYPE_TGID Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 07/11] signal: Deliver group signals via PIDTYPE_TGID not PIDTYPE_PID Eric W. Biederman
2018-07-16 12:51 ` Oleg Nesterov
2018-07-16 14:50 ` Eric W. Biederman
2018-07-16 17:17 ` Linus Torvalds
2018-07-16 18:01 ` Eric W. Biederman
2018-07-16 18:40 ` Linus Torvalds
2018-07-17 9:56 ` Oleg Nesterov
2018-07-17 10:18 ` Oleg Nesterov
2018-07-20 23:41 ` Eric W. Biederman
2018-07-17 16:38 ` Linus Torvalds
2018-07-20 23:27 ` Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 08/11] signal: Use PIDTYPE_TGID to clearly store where file signals will be sent Eric W. Biederman
2018-07-11 2:44 ` [RFC][PATCH 09/11] tty_io: Use do_send_sig_info in __do_SACK to forcibly kill tasks Eric W. Biederman
2018-07-16 14:55 ` Oleg Nesterov
2018-07-16 15:08 ` Eric W. Biederman
2018-07-16 16:50 ` Linus Torvalds
2018-07-16 19:17 ` Eric W. Biederman
2018-07-16 19:36 ` Linus Torvalds
2018-07-17 1:48 ` Eric W. Biederman
2018-07-17 10:58 ` Oleg Nesterov
2018-07-11 2:44 ` [RFC][PATCH 10/11] signal: Push pid type from signal senders down into __send_signal Eric W. Biederman
2018-07-11 3:11 ` Linus Torvalds
2018-07-11 2:44 ` [RFC][PATCH 11/11] signal: Ignore all but multi-process signals that come in during fork Eric W. Biederman
2018-07-11 14:14 ` Oleg Nesterov
2018-07-11 16:02 ` Eric W. Biederman
2018-07-12 13:42 ` Oleg Nesterov
2018-07-12 17:11 ` Eric W. Biederman
2018-07-13 14:51 ` Eric W. Biederman
2018-07-24 3:22 ` [PATCH 00/20] PIDTYPE_TGID removal of fork restarts Eric W. Biederman
2018-07-24 3:24 ` [PATCH 01/20] pids: Initialize leader_pid in init_task Eric W. Biederman
2018-07-24 3:24 ` [PATCH 02/20] pids: Move task_pid_type into sched/signal.h Eric W. Biederman
2018-07-24 3:24 ` [PATCH 03/20] pids: Compute task_tgid using signal->leader_pid Eric W. Biederman
2018-07-24 3:24 ` [PATCH 04/20] kvm: Don't open code task_pid in kvm_vcpu_ioctl Eric W. Biederman
2018-07-24 3:24 ` [PATCH 05/20] pids: Move the pgrp and session pid pointers from task_struct to signal_struct Eric W. Biederman
2018-07-24 3:24 ` [PATCH 06/20] pid: Implement PIDTYPE_TGID Eric W. Biederman
2018-07-24 3:24 ` [PATCH 07/20] signal: Use PIDTYPE_TGID to clearly store where file signals will be sent Eric W. Biederman
2018-08-16 4:04 ` [PATCH] signal: Don't send signals to tasks that don't exist Eric W. Biederman
2018-08-17 17:34 ` Dmitry Vyukov
2018-08-17 18:46 ` Eric W. Biederman
2018-08-17 19:24 ` Andrew Morton
2018-08-18 5:51 ` Eric W. Biederman
2018-08-20 19:26 ` J. Bruce Fields
2018-07-24 3:24 ` [PATCH 08/20] posix-timers: Noralize good_sigevent Eric W. Biederman
2018-07-24 3:24 ` [PATCH 09/20] signal: Pass pid and pid type into send_sigqueue Eric W. Biederman
2018-07-24 3:24 ` [PATCH 10/20] signal: Pass pid type into group_send_sig_info Eric W. Biederman
2018-07-24 3:24 ` [PATCH 11/20] signal: Pass pid type into send_sigio_to_task & send_sigurg_to_task Eric W. Biederman
2018-07-24 3:24 ` [PATCH 12/20] signal: Pass pid type into do_send_sig_info Eric W. Biederman
2018-07-24 3:24 ` [PATCH 13/20] signal: Push pid type down into send_signal Eric W. Biederman
2018-07-24 3:24 ` [PATCH 14/20] signal: Push pid type down into __send_signal Eric W. Biederman
2018-07-24 3:24 ` [PATCH 15/20] signal: Push pid type down into complete_signal Eric W. Biederman
2018-07-24 3:24 ` [PATCH 16/20] fork: Move and describe why the code examines PIDNS_ADDING Eric W. Biederman
2018-07-24 3:24 ` [PATCH 17/20] fork: Unconditionally exit if a fatal signal is pending Eric W. Biederman
2018-07-24 3:24 ` [PATCH 18/20] signal: Add calculate_sigpending() Eric W. Biederman
2018-07-26 13:20 ` Oleg Nesterov
2018-07-26 15:13 ` Eric W. Biederman [this message]
2018-07-26 16:24 ` Oleg Nesterov
2018-07-24 3:24 ` [PATCH 19/20] fork: Have new threads join on-going signal group stops Eric W. Biederman
2018-07-24 3:24 ` [PATCH 20/20] signal: Don't restart fork when signals come in Eric W. Biederman
2018-07-24 17:27 ` Linus Torvalds
2018-07-24 17:58 ` Eric W. Biederman
2018-07-24 18:29 ` Linus Torvalds
2018-07-24 20:05 ` Eric W. Biederman
2018-07-24 20:15 ` Linus Torvalds
2018-07-24 20:40 ` [PATCH v2 " Eric W. Biederman
2018-07-24 20:56 ` Linus Torvalds
2018-07-24 21:24 ` Eric W. Biederman
2018-07-25 3:56 ` [PATCH v3 " Eric W. Biederman
2018-07-26 13:41 ` Oleg Nesterov
2018-07-26 14:42 ` Eric W. Biederman
2018-07-26 15:55 ` Oleg Nesterov
2018-08-09 6:19 ` Eric W. Biederman
2018-07-26 16:21 ` Oleg Nesterov
2018-07-24 17:29 ` [PATCH 00/20] PIDTYPE_TGID removal of fork restarts Linus Torvalds
2018-07-25 16:05 ` Oleg Nesterov
2018-07-25 16:58 ` Eric W. Biederman
2018-08-09 6:53 ` [PATCH v5 0/6] Not restarting for due to signals Eric W. Biederman
2018-08-09 6:56 ` [PATCH v5 1/6] fork: Move and describe why the code examines PIDNS_ADDING Eric W. Biederman
2018-08-09 6:56 ` [PATCH v5 2/6] fork: Unconditionally exit if a fatal signal is pending Eric W. Biederman
2018-08-09 6:56 ` [PATCH v5 3/6] signal: Add calculate_sigpending() Eric W. Biederman
2018-08-09 6:56 ` [PATCH v5 4/6] fork: Skip setting TIF_SIGPENDING in ptrace_init_task Eric W. Biederman
2018-08-09 6:56 ` [PATCH v5 5/6] fork: Have new threads join on-going signal group stops Eric W. Biederman
2018-08-09 6:56 ` [PATCH v5 6/6] signal: Don't restart fork when signals come in Eric W. Biederman
2018-08-09 17:15 ` Linus Torvalds
2018-08-09 17:42 ` Eric W. Biederman
2018-08-09 18:09 ` [PATCH v6 " Eric W. Biederman
2018-08-09 17:16 ` [PATCH v5 0/6] Not restarting for due to signals Linus Torvalds
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