linux-kernel - RE: [PATCH v2] mm: hwpoison: coredump: support recovery from dump_user

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Date:   Thu, 27 Apr 2023 16:45:25 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>, Kefeng Wang <wangkefeng.wang@...wei.com>
CC:     "chu, jane" <jane.chu@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tong Tiangen <tongtiangen@...wei.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: RE: [PATCH v2] mm: hwpoison: coredump: support recovery from
 dump_user_range()

> > But in the core dump case there is no return to user. The process is being
> > terminated by the signal that leads to this core dump. So even though you
> > may consider the page being accessed to be a "user" page, you can't fix
> > it by queueing work to run on return to user.
> 
> For coredump，the task work will be called too, see following code,
> 
> get_signal
> 	sig_kernel_coredump
> 		elf_core_dump
> 			dump_user_range
> 				_copy_from_iter // with MC-safe copy, return without panic
> 	do_group_exit(ksig->info.si_signo);
> 		do_exit
> 			exit_task_work
> 				task_work_run
> 					kill_me_never
> 						memory_failure
> 

Nice. I didn't realize that the exit code path would clear any pending task_work() requests.
But it makes sense that this happens. Thanks for filling a gap in my knowledge.

-Tony