linux-kernel - Re: [PATCH] kernfs: switch global kernfs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YZbbxK1F7jY/RBFF@slm.duckdns.org>
Date:   Thu, 18 Nov 2021 13:03:32 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernfs: switch global kernfs_rwsem lock to per-fs lock

On Thu, Nov 18, 2021 at 03:00:08PM -0800, Minchan Kim wrote:
> The kernfs implementation has big lock granularity(kernfs_rwsem) so
> every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the
> lock. It makes trouble for some cases to wait the global lock
> for a long time even though they are totally independent contexts
> each other.
> 
> A general example is process A goes under direct reclaim with holding
> the lock when it accessed the file in sysfs and process B is waiting
> the lock with exclusive mode and then process C is waiting the lock
> until process B could finish the job after it gets the lock from
> process A.
> 
> This patch switches the global kernfs_rwsem to per-fs lock, which
> put the rwsem into kernfs_root.
> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

Acked-by: Tejun Heo <tj@...nel.org>

Greg, I think this is the right thing to do even if there is no concrete
performance argument (not saying there isn't). It's just weird to entangle
these completely unrelated users in a single rwsem.

Thanks.

-- 
tejun