linux-kernel - Re: shmem_recalc_inode: unable to handle kernel NULL pointer dereference

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Message-ID: <alpine.LSU.2.11.1904081014060.2770@eggly.anvils>
Date:   Mon, 8 Apr 2019 10:26:17 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
cc:     Hugh Dickins <hughd@...gle.com>,
        "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        Vineeth Pillai <vpillai@...italocean.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kelley Nielsen <kelleynnn@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Rik van Riel <riel@...riel.com>,
        Huang Ying <ying.huang@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: shmem_recalc_inode: unable to handle kernel NULL pointer
 dereference

On Mon, 8 Apr 2019, Konstantin Khlebnikov wrote:
> 
> I suppose your solution will wait for wakeup from shmem_evict_inode()?

No, it's the other way round: shmem_unuse() gets on with its work without
delay, shmem_evict_inode() waits until the stop_eviction count has gone
down to zero, saying nobody else is at work on the inode.

Waiting in shmem_evict_inode() might be more worrying, if it weren't
already packed full with lock_page()s. And less attractive with the old
quadratic style of swapoff, when shmem_evict_inode() would have freed
the inode's swap much more efficiently than swapoff could then manage.

Hugh