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SubjectRe: [PATCH 4.19 53/81] libnvdimm/btt: Fix LBA masking during free list population
Hi!

> If an implementation does happen to have it set, we would happily read
> it in as the next block to write to for writes. Since a high bit is set,
> it pushes the block number out of the range of an 'arena', and we fail
> such a write with an EIO.
>
> Follow the robustness principle, and tolerate such implementations by
> stripping out the zero flag when populating the free list during
> initialization. Additionally, use the same stripped out entries for
> detection of incomplete writes and map restoration that happens at this
> stage.

> Add a sysfs file 'log_zero_flags' that indicates the ability to accept
> such a layout to userspace applications. This enables 'ndctl
> check-namespace' to recognize whether the kernel is able to handle zero
> flags, or whether it should attempt a fix-up under the --repair
> option.

Ok, so new /sys file is added; but that should have entry in
Documentation/ and that one is not there AFAICT. (Not in -linus, so
I assume not in -stable, either).

Best regards,
Pavel

> Cc: Dan Williams <dan.j.williams@intel.com>
> Reported-by: Dexuan Cui <decui@microsoft.com>
> Reported-by: Pedro d'Aquino Filocre F S Barbuda <pbarbuda@microsoft.com>
> Tested-by: Dexuan Cui <decui@microsoft.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/nvdimm/btt.c | 25 +++++++++++++++++++------
> drivers/nvdimm/btt.h | 2 ++
> drivers/nvdimm/btt_devs.c | 8 ++++++++
> 3 files changed, 29 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
> index d78cfe82ad5c..1064a703ccec 100644
> --- a/drivers/nvdimm/btt.c
> +++ b/drivers/nvdimm/btt.c
> @@ -542,8 +542,8 @@ static int arena_clear_freelist_error(struct arena_info *arena, u32 lane)
> static int btt_freelist_init(struct arena_info *arena)
> {
> int new, ret;
> - u32 i, map_entry;
> struct log_entry log_new;
> + u32 i, map_entry, log_oldmap, log_newmap;
>
> arena->freelist = kcalloc(arena->nfree, sizeof(struct free_entry),
> GFP_KERNEL);
> @@ -555,16 +555,22 @@ static int btt_freelist_init(struct arena_info *arena)
> if (new < 0)
> return new;
>
> + /* old and new map entries with any flags stripped out */
> + log_oldmap = ent_lba(le32_to_cpu(log_new.old_map));
> + log_newmap = ent_lba(le32_to_cpu(log_new.new_map));
> +
> /* sub points to the next one to be overwritten */
> arena->freelist[i].sub = 1 - new;
> arena->freelist[i].seq = nd_inc_seq(le32_to_cpu(log_new.seq));
> - arena->freelist[i].block = le32_to_cpu(log_new.old_map);
> + arena->freelist[i].block = log_oldmap;
>
> /*
> * FIXME: if error clearing fails during init, we want to make
> * the BTT read-only
> */
> - if (ent_e_flag(log_new.old_map)) {
> + if (ent_e_flag(log_new.old_map) &&
> + !ent_normal(log_new.old_map)) {
> + arena->freelist[i].has_err = 1;
> ret = arena_clear_freelist_error(arena, i);
> if (ret)
> dev_err_ratelimited(to_dev(arena),
> @@ -572,7 +578,7 @@ static int btt_freelist_init(struct arena_info *arena)
> }
>
> /* This implies a newly created or untouched flog entry */
> - if (log_new.old_map == log_new.new_map)
> + if (log_oldmap == log_newmap)
> continue;
>
> /* Check if map recovery is needed */
> @@ -580,8 +586,15 @@ static int btt_freelist_init(struct arena_info *arena)
> NULL, NULL, 0);
> if (ret)
> return ret;
> - if ((le32_to_cpu(log_new.new_map) != map_entry) &&
> - (le32_to_cpu(log_new.old_map) == map_entry)) {
> +
> + /*
> + * The map_entry from btt_read_map is stripped of any flag bits,
> + * so use the stripped out versions from the log as well for
> + * testing whether recovery is needed. For restoration, use the
> + * 'raw' version of the log entries as that captured what we
> + * were going to write originally.
> + */
> + if ((log_newmap != map_entry) && (log_oldmap == map_entry)) {
> /*
> * Last transaction wrote the flog, but wasn't able
> * to complete the map write. So fix up the map.
> diff --git a/drivers/nvdimm/btt.h b/drivers/nvdimm/btt.h
> index db3cb6d4d0d4..ddff49c707b0 100644
> --- a/drivers/nvdimm/btt.h
> +++ b/drivers/nvdimm/btt.h
> @@ -44,6 +44,8 @@
> #define ent_e_flag(ent) (!!(ent & MAP_ERR_MASK))
> #define ent_z_flag(ent) (!!(ent & MAP_TRIM_MASK))
> #define set_e_flag(ent) (ent |= MAP_ERR_MASK)
> +/* 'normal' is both e and z flags set */
> +#define ent_normal(ent) (ent_e_flag(ent) && ent_z_flag(ent))
>
> enum btt_init_state {
> INIT_UNCHECKED = 0,
> diff --git a/drivers/nvdimm/btt_devs.c b/drivers/nvdimm/btt_devs.c
> index e341498876ca..9486acc08402 100644
> --- a/drivers/nvdimm/btt_devs.c
> +++ b/drivers/nvdimm/btt_devs.c
> @@ -159,11 +159,19 @@ static ssize_t size_show(struct device *dev,
> }
> static DEVICE_ATTR_RO(size);
>
> +static ssize_t log_zero_flags_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "Y\n");
> +}
> +static DEVICE_ATTR_RO(log_zero_flags);
> +
> static struct attribute *nd_btt_attributes[] = {
> &dev_attr_sector_size.attr,
> &dev_attr_namespace.attr,
> &dev_attr_uuid.attr,
> &dev_attr_size.attr,
> + &dev_attr_log_zero_flags.attr,
> NULL,
> };
>

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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