From: Michal Hocko <mhocko@suse.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Jan Kara <jack@suse.cz>, Hillf Danton <hdanton@sina.com>,
syzbot <syzbot+a7ab8df042baaf42ae3c@syzkaller.appspotmail.com>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs@googlegroups.com,
Tahsin Erdogan <tahsin@google.com>,
tytso@mit.edu
Subject: Re: possible deadlock in fs_reclaim_acquire (2)
Date: Thu, 11 Feb 2021 13:43:34 +0100 [thread overview]
Message-ID: <YCUmZ1SBTbDGfAN6@dhcp22.suse.cz> (raw)
In-Reply-To: <20210211114943.GH2696@kadam>
On Thu 11-02-21 14:49:43, Dan Carpenter wrote:
> On Thu, Feb 11, 2021 at 11:50:38AM +0100, 'Michal Hocko' via syzkaller-bugs wrote:
> > On Thu 11-02-21 11:22:25, Jan Kara wrote:
> > > On Thu 11-02-21 12:07:29, Hillf Danton wrote:
> >
> > I haven't received Hillf's email.
> >
> > [...]
> > > > Fix 71b565ceff37 ("ext4: drop ext4_kvmalloc()") by restoring the
> > > > GFP_NOFS introduced in dec214d00e0d ("ext4: xattr inode deduplication").
> > > >
> > > > Note this may be the fix also to possible deadlock
> > > > Reported-by: syzbot+bfdded10ab7dcd7507ae@syzkaller.appspotmail.com
> > > > https://lore.kernel.org/linux-ext4/000000000000563a0205bafb7970@google.com/
> > >
> > > Please no. Ext4 is using scoping API to limit allocations to GFP_NOFS
> > > inside transactions. In this case something didn't work which seems like a
> > > lockdep bug at the first sight but I'll talk to mm guys about it.
> > > Definitely to problem doesn't seem to be in ext4.
> >
> > Agreed. kvmalloc(NOFS) is not even supported because vmalloc doesn't
> > support GFP_KERNEL incompatible requests.
>
> Okay. I have created a new Smatch warning when people pass GFP_NOFS
> to kvmalloc() and friends. We'll see if it finds anything tomorrow.
Thanks! Let me just clarify a bit. The kvmalloc doesn't support
GFP_KERNEL incompatible requests and it simply skips vmalloc fallback.
So this is not a correctness issue. It is the API abuse though.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-02-11 13:08 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 1:25 possible deadlock in fs_reclaim_acquire (2) syzbot
[not found] ` <20210211040729.12804-1-hdanton@sina.com>
2021-02-11 10:22 ` Jan Kara
2021-02-11 10:50 ` Michal Hocko
2021-02-11 11:49 ` Dan Carpenter
2021-02-11 12:43 ` Michal Hocko [this message]
[not found] ` <20210211120424.86857A3B85@relay2.suse.de>
2021-02-11 12:12 ` Jan Kara
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