From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 3/3] xfs: use %px for data pointers when debugging
Date: Tue, 9 Jan 2018 15:16:46 -0800 [thread overview]
Message-ID: <20180109231646.GQ5602@magnolia> (raw)
In-Reply-To: <20180109230409.GP16421@dastard>
On Wed, Jan 10, 2018 at 10:04:09AM +1100, Dave Chinner wrote:
> On Tue, Jan 09, 2018 at 12:46:11PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> >
> > Starting with commit 57e734423ad ("vsprintf: refactor %pK code out of
> > pointer"), the behavior of the raw '%p' printk format specifier was
> > changed to print a 32-bit hash of the pointer value to avoid leaking
> > kernel pointers into dmesg. For most situations that's good.
> >
> > This is /undesirable/ behavior when we're trying to debug XFS, however,
> > so define a PTR_FMT that prints the actual pointer when we're in debug
> > mode.
> >
> > Note that %p for tracepoints still prints the raw pointer, so in the
> > long run we could consider rewriting some of these messages as
> > tracepoints.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
>
> It sucks to have to play games like this, but we have to be able to
> debug the code somehow....
>
> > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
> > index fd03780..0949bab 100644
> > --- a/fs/xfs/xfs_linux.h
> > +++ b/fs/xfs/xfs_linux.h
> > @@ -291,4 +291,10 @@ static inline uint64_t howmany_64(uint64_t x, uint32_t y)
> > #define XFS_IS_REALTIME_MOUNT(mp) (0)
> > #endif
> >
> > +#ifdef DEBUG
> > +# define PTR_FMT "%px"
> > +#else
> > +# define PTR_FMT "%p"
> > +#endif
>
> Can you add a comment here explaining why this is different?
/*
* Starting in Linux 4.15, the %p (raw pointer value) printk modifier
* prints a hashed version of the pointer to avoid leaking kernel
* pointers into dmesg. If we're trying to debug the kernel we want the
* raw values, so override this behavior as best we can.
*/
--D
>
> Otherwise it looks OK.
>
> Reviewed-by: Dave Chinner <dchinner@redhat.com>
> --
> Dave Chinner
> david@fromorbit.com
> --
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prev parent reply other threads:[~2018-01-09 23:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-09 20:45 [PATCH 0/3] xfs: printk fixes Darrick J. Wong
2018-01-09 20:45 ` [PATCH 1/3] xfs: change 0x%p -> %p in print messages Darrick J. Wong
2018-01-09 22:59 ` Dave Chinner
2018-01-09 20:46 ` [PATCH 2/3] xfs: use %pS printk format for direct instruction addresses Darrick J. Wong
2018-01-09 23:01 ` Dave Chinner
2018-01-09 20:46 ` [PATCH 3/3] xfs: use %px for data pointers when debugging Darrick J. Wong
2018-01-09 23:04 ` Dave Chinner
2018-01-09 23:16 ` Darrick J. Wong [this message]
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