From: Dave Chinner <david@fromorbit.com>
To: Mike Christie <mchristi@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-block@vger.kernel.org, martin@urbackup.org,
Damien.LeMoal@wdc.com
Subject: Re: [PATCH] Add prctl support for controlling PF_MEMALLOC V2
Date: Tue, 22 Oct 2019 09:52:34 +1100 [thread overview]
Message-ID: <20191021225234.GC2642@dread.disaster.area> (raw)
In-Reply-To: <20191021214137.8172-1-mchristi@redhat.com>
On Mon, Oct 21, 2019 at 04:41:37PM -0500, Mike Christie wrote:
> There are several storage drivers like dm-multipath, iscsi, tcmu-runner,
> amd nbd that have userspace components that can run in the IO path. For
> example, iscsi and nbd's userspace deamons may need to recreate a socket
> and/or send IO on it, and dm-multipath's daemon multipathd may need to
> send IO to figure out the state of paths and re-set them up.
>
> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the
> memalloc_*_save/restore functions to control the allocation behavior,
> but for userspace we would end up hitting a allocation that ended up
> writing data back to the same device we are trying to allocate for.
I think this needs to describe the symptoms this results in. i.e.
that this can result in deadlocking the IO path.
> This patch allows the userspace deamon to set the PF_MEMALLOC* flags
> with prctl during their initialization so later allocations cannot
> calling back into them.
>
> Signed-off-by: Mike Christie <mchristi@redhat.com>
> ---
....
> + case PR_SET_MEMALLOC:
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
Wouldn't CAP_SYS_RAWIO (because it's required by kernel IO path
drivers) or CAP_SYS_RESOURCE (controlling memory allocation
behaviour) be more appropriate here?
Which-ever is selected, the use should be added to the list above
the definition of the capability in include/linux/capability.h...
Otherwise looks fine to me.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2019-10-21 22:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-21 21:41 [PATCH] Add prctl support for controlling PF_MEMALLOC V2 Mike Christie
2019-10-21 22:52 ` Dave Chinner [this message]
2019-10-22 15:42 ` Mike Christie
2019-10-22 11:24 ` Michal Hocko
2019-10-22 16:13 ` Mike Christie
2019-10-22 16:33 ` Michal Hocko
2019-10-22 20:43 ` Dave Chinner
2019-10-23 7:11 ` Michal Hocko
2019-10-23 17:27 ` Mike Christie
2019-10-23 17:35 ` Michal Hocko
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