libnvdimm, btt: rework error clearing

Clearing errors or badblocks during a BTT write requires sending an ACPI
DSM, which means potentially sleeping. Since a BTT IO happens in atomic
context (preemption disabled, spinlocks may be held), we cannot perform
error clearing in the course of an IO. Due to this error clearing for
BTT IOs has hitherto been disabled.

In this patch we move error clearing out of the atomic section, and thus
re-enable error clearing with BTTs. When we are about to add a block to
the free list, we check if it was previously marked as an error, and if
it was, we add it to the freelist, but also set a flag that says error
clearing will be required. We then drop the lane (ending the atomic
context), and send a zero buffer so that the error can be cleared. The
error flag in the free list is protected by the nd 'lane', and is set
only be a thread while it holds that lane. When the error is cleared,
the flag is cleared, but while holding a mutex for that freelist index.

When writing, we check for two things -
1/ If the freelist mutex is held or if the error flag is set. If so,
this is an error block that is being (or about to be) cleared.
2/ If the block is a known badblock based on nsio->bb

The second check is required because the BTT map error flag for a map
entry only gets set when an error LBA is read. If we write to a new
location that may not have the map error flag set, but still might be in
the region's badblock list, we can trigger an EIO on the write, which is
undesirable and completely avoidable.

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/nvdimm/btt.h b/drivers/nvdimm/btt.h
index 2bc0d10b8438..578c2057524d 100644
--- a/drivers/nvdimm/btt.h
+++ b/drivers/nvdimm/btt.h
@@ -15,6 +15,7 @@
 #ifndef _LINUX_BTT_H
 #define _LINUX_BTT_H
 
+#include <linux/badblocks.h>
 #include <linux/types.h>
 
 #define BTT_SIG_LEN 16
@@ -41,6 +42,7 @@
 #define ent_lba(ent) (ent & MAP_LBA_MASK)
 #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)
 
 enum btt_init_state {
 	INIT_UNCHECKED = 0,
@@ -82,6 +84,7 @@ struct free_entry {
 	u32 block;
 	u8 sub;
 	u8 seq;
+	u8 has_err;
 };
 
 struct aligned_lock {
@@ -153,6 +156,7 @@ struct arena_info {
 	struct dentry *debugfs_dir;
 	/* Arena flags */
 	u32 flags;
+	struct mutex err_lock;
 };
 
 /**
@@ -187,6 +191,7 @@ struct btt {
 	struct mutex init_lock;
 	int init_state;
 	int num_arenas;
+	struct badblocks *phys_bb;
 };
 
 bool nd_btt_arena_is_valid(struct nd_btt *nd_btt, struct btt_sb *super);