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From: jimsiak <jimsiak@cslab.ece.ntua.gr>
To: Jinjiang Tu <tujinjiang@huawei.com>
Cc: peterx@redhat.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
	linux-mm@kvack.org, wangkefeng.wang@huawei.com
Subject: Re: Using userfaultfd with KVM's async page fault handling causes processes to hung waiting for mmap_lock to be released
Date: Fri, 07 Mar 2025 15:11:09 +0200	[thread overview]
Message-ID: <dee238e365f3727ab16d6685e186c53c@cslab.ece.ntua.gr> (raw)
In-Reply-To: <46ac83f7-d3e0-b667-7352-d853938c9fc9@huawei.com>

Hi,

 From my side, I managed to avoid the freezing of processes with the 
following change in function userfaultfd_release() in file 
fs/userfaultfd.c 
(https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L842):

I moved the following command from line 851:
WRITE_ONCE(ctx->released, true);
(https://elixir.bootlin.com/linux/v5.13/source/fs/userfaultfd.c#L851)

to line 905, that is exactly before the functions returns 0.

That simple workaround worked for my use case but I am far from sure 
that is a correct/sufficient fix for the problem at hand.

Best Regards,
Dimitris

Στις 07/03/2025 10:07, Jinjiang Tu έγραψε:
> cc Peter Xu
> 
> 在 2025/3/7 15:21, Jinjiang Tu 写道:
>> Hi,
>> 
>> I encountered the same issue too. In my scenario, GUP is called by 
>> mlockall()
>> syscall.
>> 
>> Is there a solution to fix it?
>> 
>> Thanks.
>> 


  reply	other threads:[~2025-03-07 13:11 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <79375b71-db2e-3e66-346b-254c90d915e2@cslab.ece.ntua.gr>
2023-07-19 21:16 ` Using userfaultfd with KVM's async page fault handling causes processes to hung waiting for mmap_lock to be released Axel Rasmussen
2023-07-19 21:54   ` Axel Rasmussen
2023-07-20 10:35     ` Hillf Danton
2023-07-20 20:07       ` Peter Xu
2023-07-20 20:06     ` Peter Xu
2025-03-07  7:21 ` Jinjiang Tu
2025-03-07  8:07   ` Jinjiang Tu
2025-03-07 13:11     ` jimsiak [this message]
2025-03-07 22:41       ` Peter Xu
2025-03-10  6:40         ` Jinjiang Tu
2025-03-10 18:50           ` Peter Xu
2025-03-11  8:14             ` Jinjiang Tu
2025-03-12  9:18               ` Jinjiang Tu
2025-03-12 14:09                 ` Peter Xu

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