From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Qian Cai <cai@lca.pw>,
Jeff Layton <jlayton@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
Andreas Dilger <adilger.kernel@dilger.ca>
Subject: Re: "beyond 2038" warnings from loopback mount is noisy
Date: Tue, 3 Sep 2019 19:03:25 -0400 [thread overview]
Message-ID: <20190903230324.GI2899@mit.edu> (raw)
In-Reply-To: <CABeXuvp2F4cr_77UJDYVfQ=gD8QXn+t4X3Qxs6YbyMXYJYO7mg@mail.gmail.com>
On Tue, Sep 03, 2019 at 03:47:54PM -0700, Deepa Dinamani wrote:
> > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > > index 9e3ae3be3de9..5a971d1b6d5e 100644
> > > --- a/fs/ext4/ext4.h
> > > +++ b/fs/ext4/ext4.h
> > > @@ -835,7 +835,9 @@ do {
> > > \
> > > }
> > > \
> > > else {\
> > > (raw_inode)->xtime = cpu_to_le32(clamp_t(int32_t,
> > > (inode)->xtime.tv_sec, S32_MIN, S32_MAX)); \
> > > - ext4_warning_inode(inode, "inode does not support
> > > timestamps beyond 2038"); \
> > > + if (((inode)->xtime.tv_sec != (raw_inode)->xtime) && \
> > > + ((inode)->i_sb->s_time_max > S32_MAX))
> > > \
> > > + ext4_warning_inode(inode, "inode does not
> > > support timestamps beyond 2038"); \
> > > } \
> > > } while (0)
> >
> > Sure, that's much less objectionable.
>
> The reason it was warning for every update was because of the
> ratelimiting. I think ratelimiting is not working well here. I will
> check that part.
If you are calling ext4_warning_inode() on every single update, you
really can't depend on rate limiting to prevent log spam. The problem
is sometimes we *do* need more than say, one ext4 warning every hour.
Rate limiting is a last-ditch prevention against an unintentional
denial of service attack against the system, but we can't depend on it
as license to call ext4_warning() every time we set a timestamp. That
happens essentially constantly on a running system. So if you set the
limits aggressively enough that it's not seriously annoying, it will
suppress all other potential uses of ext4_warning() --- essentially,
it will make ext4_warning useless.
The other concern I would have if that warning message is being
constantly called, post 2038, is that even *with* rate limiting, it
will turn into a massive scalability bottleneck --- remember, the
ratelimit structure has a spinlock, so even if you are suppressing
things so that we're only logging one message an hour, if it's being
called hundreds of times a second from multiple CPU's, the cache line
thrashing will make this to be a performance *nightmare*.
- Ted
next prev parent reply other threads:[~2019-09-03 23:03 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-03 15:18 "beyond 2038" warnings from loopback mount is noisy Qian Cai
2019-09-03 16:18 ` Deepa Dinamani
2019-09-03 16:36 ` Deepa Dinamani
2019-09-03 18:15 ` Qian Cai
2019-09-03 19:39 ` Andreas Dilger
2019-09-03 19:50 ` Arnd Bergmann
2019-09-03 21:13 ` Qian Cai
2019-09-03 21:17 ` Theodore Y. Ts'o
2019-09-03 21:31 ` Deepa Dinamani
2019-09-03 21:48 ` Arnd Bergmann
2019-09-03 22:38 ` Theodore Y. Ts'o
2019-09-03 22:47 ` Deepa Dinamani
2019-09-03 23:03 ` Theodore Y. Ts'o [this message]
2019-09-04 4:50 ` Deepa Dinamani
2019-09-04 12:58 ` Theodore Y. Ts'o
2019-09-04 13:21 ` Reindl Harald
2019-09-04 14:25 ` Deepa Dinamani
2019-09-03 22:16 ` Theodore Y. Ts'o
2019-09-03 21:52 ` Reindl Harald
2019-09-04 15:02 ` [PATCH] ext4: Reduce ext4 timestamp warnings Deepa Dinamani
2019-09-04 18:39 ` Andreas Dilger
2019-09-04 20:56 ` Arnd Bergmann
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