Re: [PATCH 7/7] xfs: add "fail at unmount" error handling configuration

Brian Foster
2016-05-11T14:15:55Z

On Tue, May 10, 2016 at 02:16:21PM +0200, Carlos Maiolino wrote:
> If we take "retry forever" literally on metadata IO errors, we can
> hang at unmount, once it retries those writes forever. This is the
> default behavior, unfortunately.
>
> Add an error configuration option for this behavior and default it to "fail" so
> that an unmount will trigger actuall errors, a shutdown and allow the unmount to
> succeed. It will be noisy, though, as it will log the errors and shutdown that
> occurs.
>
> To fix this, we need to mark the filesystem as being in the process of
> unmounting. Do this with a mount flag that is added at the appropriate time
> (i.e. before the blocking AIL sync). We also need to add this flag if mount
> fails after the initial phase of log recovery has been run.
>
> Changelog:
>
> V3:
> - No major changes have been done to this patch, only the ones needed to
> accomodate it on top of the remaining patches
> V4:
> - Make fail_at_unmount a global configuration option into
> ../xfs/<dev>/error directory
> - Add m_fail_unmount boolean to xfs_mount, to keep track of unmount
> error behavior
> - Create err_to_mp() helper, to translate a kobject, from m_error_kobj
> into its xfs_mount
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
> fs/xfs/xfs_buf_item.c | 4 ++++
> fs/xfs/xfs_mount.c | 12 ++++++++++++
> fs/xfs/xfs_mount.h | 2 ++
> fs/xfs/xfs_sysfs.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 64 insertions(+)
>
...
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index eda3906..1bcee7e 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
...
> @@ -1012,6 +1016,14 @@ xfs_unmountfs(
> xfs_log_force(mp, XFS_LOG_SYNC);
>
> /*
> + * We now need to tell the world we are unmounting. This will allow
> + * us to detect that the filesystem is going away and we should error
> + * out anything that we have been retrying in the background. This will
> + * prevent neverending retries iin AIL pushing from hanging the unmount.

Spelling: in

Otherwise looks good:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> + */
> + mp->m_flags |= XFS_MOUNT_UNMOUNTING;
> +
> + /*
> * Flush all pending changes from the AIL.
> */
> xfs_ail_push_all_sync(mp->m_ail);
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 72ec3e3..9063a9c 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -177,6 +177,7 @@ typedef struct xfs_mount {
> */
> __uint32_t m_generation;
>
> + bool m_fail_unmount;
> #ifdef DEBUG
> /*
> * DEBUG mode instrumentation to test and/or trigger delayed allocation
> @@ -195,6 +196,7 @@ typedef struct xfs_mount {
> #define XFS_MOUNT_WSYNC (1ULL << 0) /* for nfs - all metadata ops
> must be synchronous except
> for space allocations */
> +#define XFS_MOUNT_UNMOUNTING (1ULL << 1) /* filesystem is unmounting */
> #define XFS_MOUNT_WAS_CLEAN (1ULL << 3)
> #define XFS_MOUNT_FS_SHUTDOWN (1ULL << 4) /* atomic stop of all filesystem
> operations, typically for
> diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
> index 084a606..4c2c550 100644
> --- a/fs/xfs/xfs_sysfs.c
> +++ b/fs/xfs/xfs_sysfs.c
> @@ -381,6 +381,13 @@ to_error_cfg(struct kobject *kobject)
> return container_of(kobj, struct xfs_error_cfg, kobj);
> }
>
> +static inline struct xfs_mount *
> +err_to_mp(struct kobject *kobject)
> +{
> + struct xfs_kobj *kobj = to_kobj(kobject);
> + return container_of(kobj, struct xfs_mount, m_error_kobj);
> +}
> +
> static ssize_t
> max_retries_show(
> struct kobject *kobject,
> @@ -447,6 +454,38 @@ retry_timeout_seconds_store(
> }
> XFS_SYSFS_ATTR_RW(retry_timeout_seconds);
>
> +static ssize_t
> +fail_at_unmount_show(
> + struct kobject *kobject,
> + char *buf)
> +{
> + struct xfs_mount *mp = err_to_mp(kobject);
> +
> + return snprintf(buf, PAGE_SIZE, "%d\n", mp->m_fail_unmount);
> +}
> +
> +static ssize_t
> +fail_at_unmount_store(
> + struct kobject *kobject,
> + const char *buf,
> + size_t count)
> +{
> + struct xfs_mount *mp = err_to_mp(kobject);
> + int ret;
> + int val;
> +
> + ret = kstrtoint(buf, 0, &val);
> + if (ret)
> + return ret;
> +
> + if (val < 0 || val > 1)
> + return -EINVAL;
> +
> + mp->m_fail_unmount = val;
> + return count;
> +}
> +XFS_SYSFS_ATTR_RW(fail_at_unmount);
> +
> static struct attribute *xfs_error_attrs[] = {
> ATTR_LIST(max_retries),
> ATTR_LIST(retry_timeout_seconds),
> @@ -462,6 +501,7 @@ struct kobj_type xfs_error_cfg_ktype = {
>
> struct kobj_type xfs_error_ktype = {
> .release = xfs_sysfs_release,
> + .sysfs_ops = &xfs_sysfs_ops,
> };
>
> /*
> @@ -548,6 +588,12 @@ xfs_error_sysfs_init(
> if (error)
> return error;
>
> + error = sysfs_create_file(&mp->m_error_kobj.kobject,
> + ATTR_LIST(fail_at_unmount));
> +
> + if (error)
> + goto out_error;
> +
> /* .../xfs/<dev>/error/metadata/ */
> error = xfs_error_sysfs_init_class(mp, XFS_ERR_METADATA,
> "metadata", &mp->m_error_meta_kobj,
> --
> 2.4.11
>
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