linux-kernel - Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang in mem alloc

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Message-ID: <20181218113230.GI30879@dhcp22.suse.cz>
Date:   Tue, 18 Dec 2018 12:32:30 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Hou Tao <houtao1@...wei.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Matthew Wilcox <willy@...radead.org>, phillip@...ashfs.org.uk,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang
 in mem alloc

On Tue 18-12-18 14:06:11, Hou Tao wrote:
[...]
> In my understanding (correct me if I am wrong), there are three ways through which
> reclamation will invoked fs related code and may cause dead-lock:
> 
> (1) write-back dirty pages. Not possible for squashfs.

only from kswapd context. So not relevant to OOM killer/

> (2) the reclamation of inodes & dentries. The current file is in-use, so it will be not
>     reclaimed, and for other reclaimable inodes, squashfs_destroy_inode() will
>     be invoked and it doesn't take any locks.

There are other inodes, not only those in use. Do you use any locks that
could be taken from an inode teardown?
-- 
Michal Hocko
SUSE Labs