Re: [PATCH 2/4] libxfs: simulate system failure after a certain number of writes

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Feb 19, 2021 at 06:51:17PM -0600, Eric Sandeen wrote:
> On 2/18/21 9:18 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > Add an error injection knob so that we can simulate system failure after
> > a certain number of disk writes.  This knob is being added so that we
> > can check repair's behavior after an arbitrary number of tests.
> > 
> > Set LIBXFS_DEBUG_WRITE_CRASH={ddev,logdev,rtdev}=nn in the environment
> > to make libxfs SIGKILL itself after nn writes to the data, log, or rt
> > devices.  Note that this only applies to xfs_buf writes and zero_range.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > ---
> >  include/linux.h    |   13 ++++++++++
> >  libxfs/init.c      |   68 +++++++++++++++++++++++++++++++++++++++++++++++++---
> >  libxfs/libxfs_io.h |   19 +++++++++++++++
> >  libxfs/rdwr.c      |    6 ++++-
> >  4 files changed, 101 insertions(+), 5 deletions(-)
> > 
> > 
> > diff --git a/include/linux.h b/include/linux.h
> > index 03b3278b..7bf59e07 100644
> > --- a/include/linux.h
> > +++ b/include/linux.h
> > @@ -31,6 +31,8 @@
> >  #ifdef OVERRIDE_SYSTEM_FSXATTR
> >  # undef fsxattr
> >  #endif
> > +#include <unistd.h>
> > +#include <assert.h>
> >  
> >  static __inline__ int xfsctl(const char *path, int fd, int cmd, void *p)
> >  {
> > @@ -186,6 +188,17 @@ platform_zero_range(
> >  #define platform_zero_range(fd, s, l)	(-EOPNOTSUPP)
> >  #endif
> >  
> > +/*
> > + * Use SIGKILL to simulate an immediate program crash, without a chance to run
> > + * atexit handlers.
> > + */
> > +static inline void
> > +platform_crash(void)
> > +{
> > +	kill(getpid(), SIGKILL);
> > +	assert(0);
> > +}
> > +
> >  /*
> >   * Check whether we have to define FS_IOC_FS[GS]ETXATTR ourselves. These
> >   * are a copy of the definitions moved to linux/uapi/fs.h in the 4.5 kernel,
> > diff --git a/libxfs/init.c b/libxfs/init.c
> > index 8a8ce3c4..1ec83791 100644
> > --- a/libxfs/init.c
> > +++ b/libxfs/init.c
> > @@ -590,7 +590,8 @@ libxfs_initialize_perag(
> >  static struct xfs_buftarg *
> >  libxfs_buftarg_alloc(
> >  	struct xfs_mount	*mp,
> > -	dev_t			dev)
> > +	dev_t			dev,
> > +	unsigned long		write_fails)
> >  {
> >  	struct xfs_buftarg	*btp;
> >  
> > @@ -603,10 +604,29 @@ libxfs_buftarg_alloc(
> >  	btp->bt_mount = mp;
> >  	btp->bt_bdev = dev;
> >  	btp->flags = 0;
> > +	if (write_fails) {
> > +		btp->writes_left = write_fails;
> > +		btp->flags |= XFS_BUFTARG_INJECT_WRITE_FAIL;
> > +	}
> > +	pthread_mutex_init(&btp->lock, NULL);
> >  
> >  	return btp;
> >  }
> >  
> > +enum libxfs_write_failure_nums {
> > +	WF_DATA = 0,
> > +	WF_LOG,
> > +	WF_RT,
> > +	WF_MAX_OPTS,
> > +};
> > +
> > +static char *wf_opts[] = {
> > +	[WF_DATA]		= "ddev",
> > +	[WF_LOG]		= "logdev",
> > +	[WF_RT]			= "rtdev",
> > +	[WF_MAX_OPTS]		= NULL,
> > +};
> > +
> >  void
> >  libxfs_buftarg_init(
> >  	struct xfs_mount	*mp,
> > @@ -614,6 +634,46 @@ libxfs_buftarg_init(
> >  	dev_t			logdev,
> >  	dev_t			rtdev)
> >  {
> > +	char			*p = getenv("LIBXFS_DEBUG_WRITE_CRASH");
> > +	unsigned long		dfail = 0, lfail = 0, rfail = 0;
> > +
> > +	/* Simulate utility crash after a certain number of writes. */
> > +	while (p && *p) {
> > +		char *val;
> > +
> > +		switch (getsubopt(&p, wf_opts, &val)) {
> > +		case WF_DATA:
> > +			if (!val) {
> > +				fprintf(stderr,
> > +		_("ddev write fail requires a parameter\n"));
> > +				exit(1);
> > +			}
> > +			dfail = strtoul(val, NULL, 0);
> 
> so if we do "LIBXFS_DEBUG_WRITE_CRASH=ddev=WHEEEEEEEE!" we get back
> "dfail = 0" and nothing happens	and ... that's fine, this is a debug
> thingy.

Yep.  If you use the knob, you're expected to use it correctly.

> > +			break;
> > +		case WF_LOG:
> > +			if (!val) {
> > +				fprintf(stderr,
> > +		_("logdev write fail requires a parameter\n"));
> > +				exit(1);
> > +			}
> > +			lfail = strtoul(val, NULL, 0);
> > +			break;
> > +		case WF_RT:
> > +			if (!val) {
> > +				fprintf(stderr,
> > +		_("rtdev write fail requires a parameter\n"));
> > +				exit(1);
> > +			}
> > +			rfail = strtoul(val, NULL, 0);
> > +			break;
> > +		default:
> > +			fprintf(stderr, _("unknown write fail type %s\n"),
> > +					val);
> > +			exit(1);
> 
> although I guess we do error handling here. *shrug* don't much care,
> I guess.

Just in case we add new debug knobs in the future and fstests need a way
to detect them.

> > +			break;
> > +		}
> > +	}
> > +
> >  	if (mp->m_ddev_targp) {
> >  		/* should already have all buftargs initialised */
> >  		if (mp->m_ddev_targp->bt_bdev != dev ||
> > @@ -647,12 +707,12 @@ libxfs_buftarg_init(
> >  		return;
> >  	}
> >  
> > -	mp->m_ddev_targp = libxfs_buftarg_alloc(mp, dev);
> > +	mp->m_ddev_targp = libxfs_buftarg_alloc(mp, dev, dfail);
> >  	if (!logdev || logdev == dev)
> >  		mp->m_logdev_targp = mp->m_ddev_targp;
> >  	else
> > -		mp->m_logdev_targp = libxfs_buftarg_alloc(mp, logdev);
> > -	mp->m_rtdev_targp = libxfs_buftarg_alloc(mp, rtdev);
> > +		mp->m_logdev_targp = libxfs_buftarg_alloc(mp, logdev, lfail);
> > +	mp->m_rtdev_targp = libxfs_buftarg_alloc(mp, rtdev, rfail);
> >  }
> >  
> >  /*
> > diff --git a/libxfs/libxfs_io.h b/libxfs/libxfs_io.h
> > index c80e2d59..3cc4f4ee 100644
> > --- a/libxfs/libxfs_io.h
> > +++ b/libxfs/libxfs_io.h
> > @@ -22,6 +22,8 @@ struct xfs_perag;
> >   */
> >  struct xfs_buftarg {
> >  	struct xfs_mount	*bt_mount;
> > +	pthread_mutex_t		lock;
> > +	unsigned long		writes_left;
> >  	dev_t			bt_bdev;
> >  	unsigned int		flags;
> >  };
> > @@ -30,6 +32,23 @@ struct xfs_buftarg {
> >  #define XFS_BUFTARG_LOST_WRITE		(1 << 0)
> >  /* A dirty buffer failed the write verifier. */
> >  #define XFS_BUFTARG_CORRUPT_WRITE	(1 << 1)
> > +/* Simulate failure after a certain number of writes. */
> > +#define XFS_BUFTARG_INJECT_WRITE_FAIL	(1 << 2)
> > +
> > +/* Simulate the system crashing after a certain number of writes. */
> > +static inline void
> > +xfs_buftarg_trip_write(
> > +	struct xfs_buftarg	*btp)
> > +{
> > +	if (!(btp->flags & XFS_BUFTARG_INJECT_WRITE_FAIL))
> > +		return;
> > +
> > +	pthread_mutex_lock(&btp->lock);
> > +	btp->writes_left--;
> > +	if (!btp->writes_left)
> > +		platform_crash();
> > +	pthread_mutex_unlock(&btp->lock);
> > +}
> >  
> >  extern void	libxfs_buftarg_init(struct xfs_mount *mp, dev_t ddev,
> >  				    dev_t logdev, dev_t rtdev);
> > diff --git a/libxfs/rdwr.c b/libxfs/rdwr.c
> > index ca272387..fd456d6b 100644
> > --- a/libxfs/rdwr.c
> > +++ b/libxfs/rdwr.c
> > @@ -74,8 +74,10 @@ libxfs_device_zero(struct xfs_buftarg *btp, xfs_daddr_t start, uint len)
> >  	/* try to use special zeroing methods, fall back to writes if needed */
> >  	len_bytes = LIBXFS_BBTOOFF64(len);
> >  	error = platform_zero_range(fd, start_offset, len_bytes);
> > -	if (!error)
> > +	if (!error) {
> > +		xfs_buftarg_trip_write(btp);
> 
> Fine, but is there any real reason to catch this operation? *shrug*
> 
> >  		return 0;
> > +	}
> >  
> >  	zsize = min(BDSTRAT_SIZE, BBTOB(len));
> >  	if ((z = memalign(libxfs_device_alignment(), zsize)) == NULL) {
> > @@ -105,6 +107,7 @@ libxfs_device_zero(struct xfs_buftarg *btp, xfs_daddr_t start, uint len)
> >  				progname, __FUNCTION__);
> >  			exit(1);
> >  		}
> > +		xfs_buftarg_trip_write(btp);
> 
> I guess it's consistent with this; I wonder if we really need to trip
> in the zeroing code; it almost makes it more complex to figure out how
> many ops we want to "trip" after...  OTOH I guess you want to be able
> to test a half-completed zeroing. Hrm.

Well yes, since I was asked to write a more generic write error
injection mechanism, I decided I might as well use it for /all/ types of
writes, even if the "write" is a fancy zeroing op. :)

--D

> 
> >  		offset += bytes;
> >  	}
> >  	free(z);
> > @@ -860,6 +863,7 @@ libxfs_bwrite(
> >  	} else {
> >  		bp->b_flags |= LIBXFS_B_UPTODATE;
> >  		bp->b_flags &= ~(LIBXFS_B_DIRTY | LIBXFS_B_UNCHECKED);
> > +		xfs_buftarg_trip_write(bp->b_target);
> 
> this is where I expected the hook to go, having not considered the zeroing
> code ;)
> 
> >  	}
> >  	return bp->b_error;
> >  }
> >