Re: [PATCH 2/3] libxfs: simulate system failure after a certain number of writes

Brian Foster
2021-02-16T11:59:07Z

On Fri, Feb 12, 2021 at 09:46:56PM -0800, 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>
> ---
> libxfs/init.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++---
> libxfs/libxfs_io.h | 19 +++++++++++++++
> libxfs/rdwr.c | 6 ++++-
> 3 files changed, 88 insertions(+), 5 deletions(-)
>
>
> diff --git a/libxfs/init.c b/libxfs/init.c
> index 8a8ce3c4..1ec83791 100644
> --- a/libxfs/init.c
> +++ b/libxfs/init.c
...
> @@ -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;

Was there a reason for using an environment variable now rather than the
original command line option?

> +
> + /* 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);
> + 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);
> + break;
> + }
> + }
> +
> if (mp->m_ddev_targp) {
> /* should already have all buftargs initialised */
> if (mp->m_ddev_targp->bt_bdev != dev ||
...
> diff --git a/libxfs/libxfs_io.h b/libxfs/libxfs_io.h
> index c80e2d59..85485257 100644
> --- a/libxfs/libxfs_io.h
> +++ b/libxfs/libxfs_io.h
...
> @@ -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 write. */
> +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)
> + kill(getpid(), SIGKILL);

Can we just exit()?

(Same questions for the next patch..)

Brian

> + 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);
> 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);
> 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);
> }
> return bp->b_error;
> }
>