From: Stefan Metzmacher <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Cc: [email protected], [email protected],
[email protected]
Subject: Re: [PATCH 09/18] io-wq: fork worker threads from original task
Date: Thu, 4 Mar 2021 17:13:56 +0100 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
Am 04.03.21 um 14:19 schrieb Stefan Metzmacher:
> Hi Jens,
>
>>> Can you please explain why CLONE_SIGHAND is used here?
>>
>> We can't have CLONE_THREAD without CLONE_SIGHAND... The io-wq workers
>> don't really care about signals, we don't use them internally.
>
> I'm 100% sure, but I heard rumors that in some situations signals get
> randomly delivered to any thread of a userspace process.
Ok, from task_struct:
/* Signal handlers: */
struct signal_struct *signal;
struct sighand_struct __rcu *sighand;
sigset_t blocked;
sigset_t real_blocked;
/* Restored if set_restore_sigmask() was used: */
sigset_t saved_sigmask;
struct sigpending pending;
The signal handlers are shared, but 'blocked' is per thread/task.
> My fear was that the related logic may select a kernel thread if they
> share the same signal handlers.
I found the related logic in the interaction between
complete_signal() and wants_signal().
static inline bool wants_signal(int sig, struct task_struct *p)
{
if (sigismember(&p->blocked, sig))
return false;
...
Would it make sense to set up task->blocked to block all signals?
Something like this:
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -611,15 +611,15 @@ pid_t io_wq_fork_thread(int (*fn)(void *), void *arg)
{
unsigned long flags = CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|
CLONE_IO|SIGCHLD;
- struct kernel_clone_args args = {
- .flags = ((lower_32_bits(flags) | CLONE_VM |
- CLONE_UNTRACED) & ~CSIGNAL),
- .exit_signal = (lower_32_bits(flags) & CSIGNAL),
- .stack = (unsigned long)fn,
- .stack_size = (unsigned long)arg,
- };
+ sigset_t mask, oldmask;
+ pid_t pid;
- return kernel_clone(&args);
+ sigfillset(&mask);
+ sigprocmask(SIG_BLOCK, &mask, &oldmask);
+ pid = kernel_thread(fn, arg, flags);
+ sigprocmask(SIG_SETMASK, &oldmask, NULL);
+
+ return ret;
}
I think using kernel_thread() would be a good simplification anyway.
sig_task_ignored() has some PF_IO_WORKER logic.
Or is there any PF_IO_WORKER related logic that prevents
an io_wq thread to be excluded in complete_signal().
Or PF_IO_WORKER would teach kernel_clone to ignore CLONE_SIGHAND
and create a fresh handler and alter the copy_signal() and copy_sighand()
checks...
metze
next prev parent reply other threads:[~2021-03-04 16:15 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 17:09 [PATCHSET RFC 0/18] Remove kthread usage from io_uring Jens Axboe
2021-02-19 17:09 ` [PATCH 01/18] io_uring: remove the need for relying on an io-wq fallback worker Jens Axboe
2021-02-19 20:25 ` Eric W. Biederman
2021-02-19 20:37 ` Jens Axboe
2021-02-22 13:46 ` Pavel Begunkov
2021-02-19 17:09 ` [PATCH 02/18] io-wq: don't create any IO workers upfront Jens Axboe
2021-02-19 17:09 ` [PATCH 03/18] io_uring: disable io-wq attaching Jens Axboe
2021-02-19 17:09 ` [PATCH 04/18] io-wq: get rid of wq->use_refs Jens Axboe
2021-02-19 17:09 ` [PATCH 05/18] io_uring: tie async worker side to the task context Jens Axboe
2021-02-20 8:11 ` Hao Xu
2021-02-20 14:38 ` Jens Axboe
2021-02-21 9:16 ` Hao Xu
2021-02-19 17:09 ` [PATCH 06/18] io-wq: don't pass 'wqe' needlessly around Jens Axboe
2021-02-19 17:09 ` [PATCH 07/18] arch: setup PF_IO_WORKER threads like PF_KTHREAD Jens Axboe
2021-02-19 22:21 ` Eric W. Biederman
2021-02-19 23:26 ` Jens Axboe
2021-02-19 17:10 ` [PATCH 08/18] kernel: treat PF_IO_WORKER like PF_KTHREAD for ptrace/signals Jens Axboe
2021-02-19 17:10 ` [PATCH 09/18] io-wq: fork worker threads from original task Jens Axboe
2021-03-04 12:23 ` Stefan Metzmacher
2021-03-04 13:05 ` Jens Axboe
2021-03-04 13:19 ` Stefan Metzmacher
2021-03-04 16:13 ` Stefan Metzmacher [this message]
2021-03-04 16:42 ` Jens Axboe
2021-03-04 17:09 ` Stefan Metzmacher
2021-03-04 17:32 ` Jens Axboe
2021-03-04 18:19 ` Jens Axboe
2021-03-04 18:56 ` Linus Torvalds
2021-03-04 19:19 ` Jens Axboe
2021-03-04 19:46 ` Linus Torvalds
2021-03-04 19:54 ` Jens Axboe
2021-03-04 20:00 ` Jens Axboe
2021-03-04 20:23 ` Jens Axboe
2021-03-04 20:50 ` Linus Torvalds
2021-03-04 20:54 ` Jens Axboe
2021-03-05 19:16 ` Eric W. Biederman
2021-03-05 19:00 ` Eric W. Biederman
2021-02-19 17:10 ` [PATCH 10/18] io-wq: worker idling always returns false Jens Axboe
2021-02-19 17:10 ` [PATCH 11/18] io_uring: remove any grabbing of context Jens Axboe
2021-02-19 17:10 ` [PATCH 12/18] io_uring: remove io_identity Jens Axboe
2021-02-19 17:10 ` [PATCH 13/18] io-wq: only remove worker from free_list, if it was there Jens Axboe
2021-02-19 17:10 ` [PATCH 14/18] io-wq: make io_wq_fork_thread() available to other users Jens Axboe
2021-02-19 17:10 ` [PATCH 15/18] io_uring: move SQPOLL thread io-wq forked worker Jens Axboe
2021-02-19 17:10 ` [PATCH 16/18] Revert "proc: don't allow async path resolution of /proc/thread-self components" Jens Axboe
2021-02-19 17:10 ` [PATCH 17/18] Revert "proc: don't allow async path resolution of /proc/self components" Jens Axboe
2021-02-19 17:10 ` [PATCH 18/18] net: remove cmsg restriction from io_uring based send/recvmsg calls Jens Axboe
2021-02-19 23:44 ` [PATCHSET RFC 0/18] Remove kthread usage from io_uring Stefan Metzmacher
2021-02-19 23:51 ` Jens Axboe
2021-02-21 5:04 ` Linus Torvalds
2021-02-21 21:22 ` Jens Axboe
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