Hello Coly,
Saturday, January 27, 2018, 5:24:06 PM, you wrote:
> Current bcache failure handling code will stop all attached bcache devices
> when the cache set is broken or disconnected. This is desired behavior for
> most of enterprise or cloud use cases, but maybe not for low end
> configuration. Nix <nix@xxxxxxxxxxxxx> points out, users may still want to
> access the bcache device after cache device failed, for example on laptops.
In the current state, this functionality is rather user-unfriendly.
1. The new "stop_when_cache_set_failed" option doesn't seem to be persistent.
(At least, I did not see any explicit mechanism of saving/restoring it.) That
is, users will have to set it on each system startup.
2. If the new option is set to zero, it will (supposedly) lead to data
corruption/loss when cache set of a "dirty" bcache device is detached. The
option that an average home user may want to switch shouldn't be a way to
shoot oneself in the foot!
As a remedy, the option could be changed to have the states "always" and
"auto" instead of "1" and "0", so that "auto" would still stop the bcache
device if it (or the entire cache set) is "dirty". (Alternatively, it could be
renamed to "force_stop_when_cache_set_failed" or
"always_stop_when_cache_set_failed" with values "1" and "0", if string values
are undesirable.)
Also, the printed warning is somewhat misleading: it says "To disable this
warning message, please set /sys/block/%s/bcache/stop_when_cache_set_failed to
1", whereas the suggested change would lead to behaviour change rather that to
just disabling the warning.
3. If (2) is implemented, the default value for the option could be changed to
"auto". (The rationale is that enterprise users who want it enabled are better
prepared to tune their device settings on startup.) However, this is only
important if (1) is not implemented.
> This patch adds a per-cached_dev option stop_when_cache_set_failed, which
> is enabled (1) by default. Its value can be set via sysfs, when it is set
> to 0, the corresponding bcache device won't be stopped when a broken
> or disconnected cache set is retiring.
> When the cached device has dirty data on retiring cache set, if bcache
> device is not stopped, following I/O request on the bcache device may
> result data corruption on backing device. This patch also prints out warn-
> ing information in kernel message.
> Signed-off-by: Coly Li <colyli@xxxxxxx>
> Cc: Nix <nix@xxxxxxxxxxxxx>
> Cc: Michael Lyle <mlyle@xxxxxxxx>
> Cc: Junhui Tang <tang.junhui@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> ---
> drivers/md/bcache/bcache.h | 1 +
> drivers/md/bcache/super.c | 63
> +++++++++++++++++++++++++++++++++-------------
> drivers/md/bcache/sysfs.c | 10 ++++++++
> 3 files changed, 56 insertions(+), 18 deletions(-)
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 9eedb35d01bc..3756a196916f 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -362,6 +362,7 @@ struct cached_dev {
> unsigned readahead;
>
> unsigned io_disable:1;
> + unsigned stop_when_cache_set_failed:1;
> unsigned verify:1;
> unsigned bypass_torture_test:1;
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 85adf1e29d11..93f720433b40 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1246,6 +1246,7 @@ static int cached_dev_init(struct cached_dev *dc, unsigned block_size)
> atomic_set(&dc->io_errors, 0);
> dc->io_disable = false;
> dc->error_limit = DEFAULT_CACHED_DEV_ERROR_LIMIT;
+ dc->>stop_when_cache_set_failed = 1;
>
> bch_cached_dev_request_init(dc);
> bch_cached_dev_writeback_init(dc);
> @@ -1541,33 +1542,59 @@ static void cache_set_flush(struct closure *cl)
> closure_return(cl);
> }
>
> +/*
+ * dc->>stop_when_cache_set_failed is default to true. If it is explicitly
> + * set to false by user, the bcache device won't be stopped when cache set
> + * is broken or disconnected. If there is dirty data on failed cache set,
> + * not stopping bcache device may result data corruption on backing device,
> + * pr_warn() notices the protential risk in kernel message.
> + */
> +static void try_stop_bcache_device(struct cache_set *c,
> + struct bcache_device *d,
> + struct cached_dev *dc)
> +{
+ if (dc->>stop_when_cache_set_failed)
> + bcache_device_stop(d);
> + else if (!dc->stop_when_cache_set_failed &&
> + atomic_read(&dc->has_dirty))
> + pr_warn("bcache: device %s won't be stopped while unregistering"
> + " broken dirty cache set %pU, your data has potential "
> + "risk to be corrupted. To disable this warning message,"
> + " please set /sys/block/%s/bcache/stop_when_"
> + "cache_set_failed to 1.",
> + d->name, c->sb.set_uuid, d->name);
> +}
> +
> static void __cache_set_unregister(struct closure *cl)
> {
> struct cache_set *c = container_of(cl, struct cache_set, caching);
> struct cached_dev *dc;
> + struct bcache_device *d;
> size_t i;
>
> mutex_lock(&bch_register_lock);
>
> - for (i = 0; i < c->devices_max_used; i++)
> - if (c->devices[i]) {
> - if (!UUID_FLASH_ONLY(&c->uuids[i]) &&
> - test_bit(CACHE_SET_UNREGISTERING, &c->flags)) {
> - dc = container_of(c->devices[i],
> - struct cached_dev, disk);
> - bch_cached_dev_detach(dc);
> - /*
> - * If we come here by too many I/O errors,
> - * bcache device should be stopped too, to
> - * keep data consistency on cache and
> - * backing devices.
> - */
> - if (test_bit(CACHE_SET_IO_DISABLE, &c->flags))
> - bcache_device_stop(c->devices[i]);
> - } else {
> - bcache_device_stop(c->devices[i]);
> - }
> + for (i = 0; i < c->devices_max_used; i++) {
> + d = c->devices[i];
> + if (!d)
> + continue;
> +
> + if (!UUID_FLASH_ONLY(&c->uuids[i]) &&
> + test_bit(CACHE_SET_UNREGISTERING, &c->flags)) {
> + dc = container_of(d, struct cached_dev, disk);
> + bch_cached_dev_detach(dc);
> + /*
> + * If we come here by too many I/O errors,
> + * bcache device should be stopped too, to
> + * keep data consistency on cache and
> + * backing devices.
> + */
> + if (test_bit(CACHE_SET_IO_DISABLE, &c->flags))
> + try_stop_bcache_device(c, d, dc);
> + } else {
> + bcache_device_stop(d);
> }
> + }
>
> mutex_unlock(&bch_register_lock);
>
> diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
> index 7288927f2a47..b096d4c37c9b 100644
> --- a/drivers/md/bcache/sysfs.c
> +++ b/drivers/md/bcache/sysfs.c
> @@ -93,6 +93,7 @@ read_attribute(partial_stripes_expensive);
> rw_attribute(synchronous);
> rw_attribute(journal_delay_ms);
> rw_attribute(io_disable);
> +rw_attribute(stop_when_cache_set_failed);
> rw_attribute(discard);
> rw_attribute(running);
> rw_attribute(label);
> @@ -134,6 +135,8 @@ SHOW(__bch_cached_dev)
> sysfs_hprint(io_errors, atomic_read(&dc->io_errors));
> sysfs_printf(io_error_limit, "%i", dc->error_limit);
> sysfs_printf(io_disable, "%i", dc->io_disable);
> + sysfs_printf(stop_when_cache_set_failed, "%i",
> + dc->stop_when_cache_set_failed);
> var_print(writeback_rate_update_seconds);
> var_print(writeback_rate_i_term_inverse);
> var_print(writeback_rate_p_term_inverse);
> @@ -233,6 +236,12 @@ STORE(__cached_dev)
> dc->io_disable = v ? 1 : 0;
> }
>
> + if (attr == &sysfs_stop_when_cache_set_failed) {
> + int v = strtoul_or_return(buf);
> +
+ dc->>stop_when_cache_set_failed = v ? 1 : 0;
> + }
> +
> d_strtoi_h(sequential_cutoff);
> d_strtoi_h(readahead);
>
> @@ -343,6 +352,7 @@ static struct attribute *bch_cached_dev_files[] = {
> &sysfs_errors,
> &sysfs_io_error_limit,
> &sysfs_io_disable,
> + &sysfs_stop_when_cache_set_failed,
> &sysfs_dirty_data,
> &sysfs_stripe_size,
> &sysfs_partial_stripes_expensive,
Pavel Goran
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
