Merge tag 'pstore-v4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull pstore updates from Kees Cook:
 "Improvements and refactorings:

   - Improve compression handling

   - Refactor argument handling during initialization

   - Avoid needless locking for saner EFI backend handling

   - Add more kern-doc and improve debugging output"

* tag 'pstore-v4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  pstore/ram: Avoid NULL deref in ftrace merging failure path
  pstore: Convert buf_lock to semaphore
  pstore: Fix bool initialization/comparison
  pstore/ram: Do not treat empty buffers as valid
  pstore/ram: Simplify ramoops_get_next_prz() arguments
  pstore: Map PSTORE_TYPE_* to strings
  pstore: Replace open-coded << with BIT()
  pstore: Improve and update some comments and status output
  pstore/ram: Add kern-doc for struct persistent_ram_zone
  pstore/ram: Report backend assignments with finer granularity
  pstore/ram: Standardize module name in ramoops
  pstore: Avoid duplicate call of persistent_ram_zap()
  pstore: Remove needless lock during console writes
  pstore: Do not use crash buffer for decompression

5 files changed, 160 insertions, 174 deletions

diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
index 06aab07b6bb7..b8a0931568f8 100644
--- a/fs/pstore/ftrace.c
+++ b/fs/pstore/ftrace.c
@@ -148,7 +148,7 @@ void pstore_unregister_ftrace(void)
 	mutex_lock(&pstore_ftrace_lock);
 	if (pstore_ftrace_enabled) {
 		unregister_ftrace_function(&pstore_ftrace_ops);
-		pstore_ftrace_enabled = 0;
+		pstore_ftrace_enabled = false;
 	}
 	mutex_unlock(&pstore_ftrace_lock);
 
diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index 8cf2218b46a7..c60ee46f3e39 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -335,53 +335,10 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 		goto fail_alloc;
 	private->record = record;
 
-	switch (record->type) {
-	case PSTORE_TYPE_DMESG:
-		scnprintf(name, sizeof(name), "dmesg-%s-%llu%s",
-			  record->psi->name, record->id,
-			  record->compressed ? ".enc.z" : "");
-		break;
-	case PSTORE_TYPE_CONSOLE:
-		scnprintf(name, sizeof(name), "console-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_FTRACE:
-		scnprintf(name, sizeof(name), "ftrace-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_MCE:
-		scnprintf(name, sizeof(name), "mce-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_PPC_RTAS:
-		scnprintf(name, sizeof(name), "rtas-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_PPC_OF:
-		scnprintf(name, sizeof(name), "powerpc-ofw-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_PPC_COMMON:
-		scnprintf(name, sizeof(name), "powerpc-common-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_PMSG:
-		scnprintf(name, sizeof(name), "pmsg-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_PPC_OPAL:
-		scnprintf(name, sizeof(name), "powerpc-opal-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	case PSTORE_TYPE_UNKNOWN:
-		scnprintf(name, sizeof(name), "unknown-%s-%llu",
-			  record->psi->name, record->id);
-		break;
-	default:
-		scnprintf(name, sizeof(name), "type%d-%s-%llu",
-			  record->type, record->psi->name, record->id);
-		break;
-	}
+	scnprintf(name, sizeof(name), "%s-%s-%llu%s",
+			pstore_type_to_name(record->type),
+			record->psi->name, record->id,
+			record->compressed ? ".enc.z" : "");
 
 	dentry = d_alloc_name(root, name);
 	if (!dentry)
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index b821054ca3ed..2d1066ed3c28 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -59,6 +59,19 @@ MODULE_PARM_DESC(update_ms, "milliseconds before pstore updates its content "
 		 "enabling this option is not safe, it may lead to further "
 		 "corruption on Oopses)");
 
+/* Names should be in the same order as the enum pstore_type_id */
+static const char * const pstore_type_names[] = {
+	"dmesg",
+	"mce",
+	"console",
+	"ftrace",
+	"rtas",
+	"powerpc-ofw",
+	"powerpc-common",
+	"pmsg",
+	"powerpc-opal",
+};
+
 static int pstore_new_entry;
 
 static void pstore_timefunc(struct timer_list *);
@@ -104,6 +117,30 @@ void pstore_set_kmsg_bytes(int bytes)
 /* Tag each group of saved records with a sequence number */
 static int	oopscount;
 
+const char *pstore_type_to_name(enum pstore_type_id type)
+{
+	BUILD_BUG_ON(ARRAY_SIZE(pstore_type_names) != PSTORE_TYPE_MAX);
+
+	if (WARN_ON_ONCE(type >= PSTORE_TYPE_MAX))
+		return "unknown";
+
+	return pstore_type_names[type];
+}
+EXPORT_SYMBOL_GPL(pstore_type_to_name);
+
+enum pstore_type_id pstore_name_to_type(const char *name)
+{
+	int i;
+
+	for (i = 0; i < PSTORE_TYPE_MAX; i++) {
+		if (!strcmp(pstore_type_names[i], name))
+			return i;
+	}
+
+	return PSTORE_TYPE_MAX;
+}
+EXPORT_SYMBOL_GPL(pstore_name_to_type);
+
 static const char *get_reason_str(enum kmsg_dump_reason reason)
 {
 	switch (reason) {
@@ -124,26 +161,27 @@ static const char *get_reason_str(enum kmsg_dump_reason reason)
 	}
 }
 
-bool pstore_cannot_block_path(enum kmsg_dump_reason reason)
+/*
+ * Should pstore_dump() wait for a concurrent pstore_dump()? If
+ * not, the current pstore_dump() will report a failure to dump
+ * and return.
+ */
+static bool pstore_cannot_wait(enum kmsg_dump_reason reason)
 {
-	/*
-	 * In case of NMI path, pstore shouldn't be blocked
-	 * regardless of reason.
-	 */
+	/* In NMI path, pstore shouldn't block regardless of reason. */
 	if (in_nmi())
 		return true;
 
 	switch (reason) {
 	/* In panic case, other cpus are stopped by smp_send_stop(). */
 	case KMSG_DUMP_PANIC:
-	/* Emergency restart shouldn't be blocked by spin lock. */
+	/* Emergency restart shouldn't be blocked. */
 	case KMSG_DUMP_EMERG:
 		return true;
 	default:
 		return false;
 	}
 }
-EXPORT_SYMBOL_GPL(pstore_cannot_block_path);
 
 #if IS_ENABLED(CONFIG_PSTORE_DEFLATE_COMPRESS)
 static int zbufsize_deflate(size_t size)
@@ -258,20 +296,6 @@ static int pstore_compress(const void *in, void *out,
 	return outlen;
 }
 
-static int pstore_decompress(void *in, void *out,
-			     unsigned int inlen, unsigned int outlen)
-{
-	int ret;
-
-	ret = crypto_comp_decompress(tfm, in, inlen, out, &outlen);
-	if (ret) {
-		pr_err("crypto_comp_decompress failed, ret = %d!\n", ret);
-		return ret;
-	}
-
-	return outlen;
-}
-
 static void allocate_buf_for_compression(void)
 {
 	struct crypto_comp *ctx;
@@ -318,7 +342,7 @@ static void allocate_buf_for_compression(void)
 	big_oops_buf_sz = size;
 	big_oops_buf = buf;
 
-	pr_info("Using compression: %s\n", zbackend->name);
+	pr_info("Using crash dump compression: %s\n", zbackend->name);
 }
 
 static void free_buf_for_compression(void)
@@ -368,9 +392,8 @@ void pstore_record_init(struct pstore_record *record,
 }
 
 /*
- * callback from kmsg_dump. (s2,l2) has the most recently
- * written bytes, older bytes are in (s1,l1). Save as much
- * as we can from the end of the buffer.
+ * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
+ * end of the buffer.
  */
 static void pstore_dump(struct kmsg_dumper *dumper,
 			enum kmsg_dump_reason reason)
@@ -378,23 +401,23 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
-	unsigned long	flags = 0;
-	int		is_locked;
 	int		ret;
 
 	why = get_reason_str(reason);
 
-	if (pstore_cannot_block_path(reason)) {
-		is_locked = spin_trylock_irqsave(&psinfo->buf_lock, flags);
-		if (!is_locked) {
-			pr_err("pstore dump routine blocked in %s path, may corrupt error record\n"
-				       , in_nmi() ? "NMI" : why);
+	if (down_trylock(&psinfo->buf_lock)) {
+		/* Failed to acquire lock: give up if we cannot wait. */
+		if (pstore_cannot_wait(reason)) {
+			pr_err("dump skipped in %s path: may corrupt error record\n",
+				in_nmi() ? "NMI" : why);
+			return;
+		}
+		if (down_interruptible(&psinfo->buf_lock)) {
+			pr_err("could not grab semaphore?!\n");
 			return;
 		}
-	} else {
-		spin_lock_irqsave(&psinfo->buf_lock, flags);
-		is_locked = 1;
 	}
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -411,7 +434,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		record.part = part;
 		record.buf = psinfo->buf;
 
-		if (big_oops_buf && is_locked) {
+		if (big_oops_buf) {
 			dst = big_oops_buf;
 			dst_size = big_oops_buf_sz;
 		} else {
@@ -429,7 +452,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 					  dst_size, &dump_size))
 			break;
 
-		if (big_oops_buf && is_locked) {
+		if (big_oops_buf) {
 			zipped_len = pstore_compress(dst, psinfo->buf,
 						header_size + dump_size,
 						psinfo->bufsize);
@@ -452,8 +475,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		total += record.size;
 		part++;
 	}
-	if (is_locked)
-		spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+
+	up(&psinfo->buf_lock);
 }
 
 static struct kmsg_dumper pstore_dumper = {
@@ -476,31 +499,14 @@ static void pstore_unregister_kmsg(void)
 #ifdef CONFIG_PSTORE_CONSOLE
 static void pstore_console_write(struct console *con, const char *s, unsigned c)
 {
-	const char *e = s + c;
-
-	while (s < e) {
-		struct pstore_record record;
-		unsigned long flags;
+	struct pstore_record record;
 
-		pstore_record_init(&record, psinfo);
-		record.type = PSTORE_TYPE_CONSOLE;
-
-		if (c > psinfo->bufsize)
-			c = psinfo->bufsize;
+	pstore_record_init(&record, psinfo);
+	record.type = PSTORE_TYPE_CONSOLE;
 
-		if (oops_in_progress) {
-			if (!spin_trylock_irqsave(&psinfo->buf_lock, flags))
-				break;
-		} else {
-			spin_lock_irqsave(&psinfo->buf_lock, flags);
-		}
-		record.buf = (char *)s;
-		record.size = c;
-		psinfo->write(&record);
-		spin_unlock_irqrestore(&psinfo->buf_lock, flags);
-		s += c;
-		c = e - s;
-	}
+	record.buf = (char *)s;
+	record.size = c;
+	psinfo->write(&record);
 }
 
 static struct console pstore_console = {
@@ -589,6 +595,7 @@ int pstore_register(struct pstore_info *psi)
 		psi->write_user = pstore_write_user_compat;
 	psinfo = psi;
 	mutex_init(&psinfo->read_mutex);
+	sema_init(&psinfo->buf_lock, 1);
 	spin_unlock(&pstore_lock);
 
 	if (owner && !try_module_get(owner)) {
@@ -656,8 +663,9 @@ EXPORT_SYMBOL_GPL(pstore_unregister);
 
 static void decompress_record(struct pstore_record *record)
 {
+	int ret;
 	int unzipped_len;
-	char *decompressed;
+	char *unzipped, *workspace;
 
 	if (!record->compressed)
 		return;
@@ -668,35 +676,42 @@ static void decompress_record(struct pstore_record *record)
 		return;
 	}
 
-	/* No compression method has created the common buffer. */
+	/* Missing compression buffer means compression was not initialized. */
 	if (!big_oops_buf) {
-		pr_warn("no decompression buffer allocated\n");
+		pr_warn("no decompression method initialized!\n");
 		return;
 	}
 
-	unzipped_len = pstore_decompress(record->buf, big_oops_buf,
-					 record->size, big_oops_buf_sz);
-	if (unzipped_len <= 0) {
-		pr_err("decompression failed: %d\n", unzipped_len);
+	/* Allocate enough space to hold max decompression and ECC. */
+	unzipped_len = big_oops_buf_sz;
+	workspace = kmalloc(unzipped_len + record->ecc_notice_size,
+			    GFP_KERNEL);
+	if (!workspace)
 		return;
-	}
 
-	/* Build new buffer for decompressed contents. */
-	decompressed = kmalloc(unzipped_len + record->ecc_notice_size,
-			       GFP_KERNEL);
-	if (!decompressed) {
-		pr_err("decompression ran out of memory\n");
+	/* After decompression "unzipped_len" is almost certainly smaller. */
+	ret = crypto_comp_decompress(tfm, record->buf, record->size,
+					  workspace, &unzipped_len);
+	if (ret) {
+		pr_err("crypto_comp_decompress failed, ret = %d!\n", ret);
+		kfree(workspace);
 		return;
 	}
-	memcpy(decompressed, big_oops_buf, unzipped_len);
 
 	/* Append ECC notice to decompressed buffer. */
-	memcpy(decompressed + unzipped_len, record->buf + record->size,
+	memcpy(workspace + unzipped_len, record->buf + record->size,
 	       record->ecc_notice_size);
 
-	/* Swap out compresed contents with decompressed contents. */
+	/* Copy decompressed contents into an minimum-sized allocation. */
+	unzipped = kmemdup(workspace, unzipped_len + record->ecc_notice_size,
+			   GFP_KERNEL);
+	kfree(workspace);
+	if (!unzipped)
+		return;
+
+	/* Swap out compressed contents with decompressed contents. */
 	kfree(record->buf);
-	record->buf = decompressed;
+	record->buf = unzipped;
 	record->size = unzipped_len;
 	record->compressed = false;
 }
diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index e02a9039b5ea..96f7d32cd184 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -124,19 +124,17 @@ static int ramoops_pstore_open(struct pstore_info *psi)
 }
 
 static struct persistent_ram_zone *
-ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
-		     u64 *id,
-		     enum pstore_type_id *typep, enum pstore_type_id type,
-		     bool update)
+ramoops_get_next_prz(struct persistent_ram_zone *przs[], int id,
+		     struct pstore_record *record)
 {
 	struct persistent_ram_zone *prz;
-	int i = (*c)++;
+	bool update = (record->type == PSTORE_TYPE_DMESG);
 
 	/* Give up if we never existed or have hit the end. */
-	if (!przs || i >= max)
+	if (!przs)
 		return NULL;
 
-	prz = przs[i];
+	prz = przs[id];
 	if (!prz)
 		return NULL;
 
@@ -147,8 +145,8 @@ ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
 	if (!persistent_ram_old_size(prz))
 		return NULL;
 
-	*typep = type;
-	*id = i;
+	record->type = prz->type;
+	record->id = id;
 
 	return prz;
 }
@@ -255,10 +253,8 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 
 	/* Find the next valid persistent_ram_zone for DMESG */
 	while (cxt->dump_read_cnt < cxt->max_dump_cnt && !prz) {
-		prz = ramoops_get_next_prz(cxt->dprzs, &cxt->dump_read_cnt,
-					   cxt->max_dump_cnt, &record->id,
-					   &record->type,
-					   PSTORE_TYPE_DMESG, 1);
+		prz = ramoops_get_next_prz(cxt->dprzs, cxt->dump_read_cnt++,
+					   record);
 		if (!prz_ok(prz))
 			continue;
 		header_length = ramoops_read_kmsg_hdr(persistent_ram_old(prz),
@@ -272,22 +268,18 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 		}
 	}
 
-	if (!prz_ok(prz))
-		prz = ramoops_get_next_prz(&cxt->cprz, &cxt->console_read_cnt,
-					   1, &record->id, &record->type,
-					   PSTORE_TYPE_CONSOLE, 0);
+	if (!prz_ok(prz) && !cxt->console_read_cnt++)
+		prz = ramoops_get_next_prz(&cxt->cprz, 0 /* single */, record);
 
-	if (!prz_ok(prz))
-		prz = ramoops_get_next_prz(&cxt->mprz, &cxt->pmsg_read_cnt,
-					   1, &record->id, &record->type,
-					   PSTORE_TYPE_PMSG, 0);
+	if (!prz_ok(prz) && !cxt->pmsg_read_cnt++)
+		prz = ramoops_get_next_prz(&cxt->mprz, 0 /* single */, record);
 
 	/* ftrace is last since it may want to dynamically allocate memory. */
 	if (!prz_ok(prz)) {
-		if (!(cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)) {
-			prz = ramoops_get_next_prz(cxt->fprzs,
-					&cxt->ftrace_read_cnt, 1, &record->id,
-					&record->type, PSTORE_TYPE_FTRACE, 0);
+		if (!(cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU) &&
+		    !cxt->ftrace_read_cnt++) {
+			prz = ramoops_get_next_prz(cxt->fprzs, 0 /* single */,
+						   record);
 		} else {
 			/*
 			 * Build a new dummy record which combines all the
@@ -299,15 +291,12 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 					  GFP_KERNEL);
 			if (!tmp_prz)
 				return -ENOMEM;
+			prz = tmp_prz;
 			free_prz = true;
 
 			while (cxt->ftrace_read_cnt < cxt->max_ftrace_cnt) {
 				prz_next = ramoops_get_next_prz(cxt->fprzs,
-						&cxt->ftrace_read_cnt,
-						cxt->max_ftrace_cnt,
-						&record->id,
-						&record->type,
-						PSTORE_TYPE_FTRACE, 0);
+						cxt->ftrace_read_cnt++, record);
 
 				if (!prz_ok(prz_next))
 					continue;
@@ -321,7 +310,6 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 					goto out;
 			}
 			record->id = 0;
-			prz = tmp_prz;
 		}
 	}
 
@@ -611,6 +599,7 @@ static int ramoops_init_przs(const char *name,
 			goto fail;
 		}
 		*paddr += zone_sz;
+		prz_ar[i]->type = pstore_name_to_type(name);
 	}
 
 	*przs = prz_ar;
@@ -640,7 +629,7 @@ static int ramoops_init_prz(const char *name,
 
 	label = kasprintf(GFP_KERNEL, "ramoops:%s", name);
 	*prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
-				  cxt->memtype, 0, label);
+				  cxt->memtype, PRZ_FLAG_ZAP_OLD, label);
 	if (IS_ERR(*prz)) {
 		int err = PTR_ERR(*prz);
 
@@ -649,9 +638,8 @@ static int ramoops_init_prz(const char *name,
 		return err;
 	}
 
-	persistent_ram_zap(*prz);
-
 	*paddr += sz;
+	(*prz)->type = pstore_name_to_type(name);
 
 	return 0;
 }
@@ -787,7 +775,7 @@ static int ramoops_probe(struct platform_device *pdev)
 
 	dump_mem_sz = cxt->size - cxt->console_size - cxt->ftrace_size
 			- cxt->pmsg_size;
-	err = ramoops_init_przs("dump", dev, cxt, &cxt->dprzs, &paddr,
+	err = ramoops_init_przs("dmesg", dev, cxt, &cxt->dprzs, &paddr,
 				dump_mem_sz, cxt->record_size,
 				&cxt->max_dump_cnt, 0, 0);
 	if (err)
@@ -827,7 +815,6 @@ static int ramoops_probe(struct platform_device *pdev)
 		err = -ENOMEM;
 		goto fail_clear;
 	}
-	spin_lock_init(&cxt->pstore.buf_lock);
 
 	cxt->pstore.flags = PSTORE_FLAGS_DMESG;
 	if (cxt->console_size)
@@ -855,9 +842,9 @@ static int ramoops_probe(struct platform_device *pdev)
 	ramoops_pmsg_size = pdata->pmsg_size;
 	ramoops_ftrace_size = pdata->ftrace_size;
 
-	pr_info("attached 0x%lx@0x%llx, ecc: %d/%d\n",
+	pr_info("using 0x%lx@0x%llx, ecc: %d\n",
 		cxt->size, (unsigned long long)cxt->phys_addr,
-		cxt->ecc_info.ecc_size, cxt->ecc_info.block_size);
+		cxt->ecc_info.ecc_size);
 
 	return 0;
 
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index 12e21f789194..c11711c2cc83 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -12,7 +12,7 @@
  *
  */
 
-#define pr_fmt(fmt) "persistent_ram: " fmt
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/device.h>
 #include <linux/err.h>
@@ -29,6 +29,16 @@
 #include <linux/vmalloc.h>
 #include <asm/page.h>
 
+/**
+ * struct persistent_ram_buffer - persistent circular RAM buffer
+ *
+ * @sig:
+ *	signature to indicate header (PERSISTENT_RAM_SIG xor PRZ-type value)
+ * @start:
+ *	offset into @data where the beginning of the stored bytes begin
+ * @size:
+ *	number of valid bytes stored in @data
+ */
 struct persistent_ram_buffer {
 	uint32_t    sig;
 	atomic_t    start;
@@ -443,7 +453,8 @@ static void *persistent_ram_iomap(phys_addr_t start, size_t size,
 	void *va;
 
 	if (!request_mem_region(start, size, label ?: "ramoops")) {
-		pr_err("request mem region (0x%llx@0x%llx) failed\n",
+		pr_err("request mem region (%s 0x%llx@0x%llx) failed\n",
+			label ?: "ramoops",
 			(unsigned long long)size, (unsigned long long)start);
 		return NULL;
 	}
@@ -489,32 +500,42 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
 				    struct persistent_ram_ecc_info *ecc_info)
 {
 	int ret;
+	bool zap = !!(prz->flags & PRZ_FLAG_ZAP_OLD);
 
 	ret = persistent_ram_init_ecc(prz, ecc_info);
-	if (ret)
+	if (ret) {
+		pr_warn("ECC failed %s\n", prz->label);
 		return ret;
+	}
 
 	sig ^= PERSISTENT_RAM_SIG;
 
 	if (prz->buffer->sig == sig) {
+		if (buffer_size(prz) == 0) {
+			pr_debug("found existing empty buffer\n");
+			return 0;
+		}
+
 		if (buffer_size(prz) > prz->buffer_size ||
-		    buffer_start(prz) > buffer_size(prz))
+		    buffer_start(prz) > buffer_size(prz)) {
 			pr_info("found existing invalid buffer, size %zu, start %zu\n",
 				buffer_size(prz), buffer_start(prz));
-		else {
+			zap = true;
+		} else {
 			pr_debug("found existing buffer, size %zu, start %zu\n",
 				 buffer_size(prz), buffer_start(prz));
 			persistent_ram_save_old(prz);
-			return 0;
 		}
 	} else {
 		pr_debug("no valid data in buffer (sig = 0x%08x)\n",
 			 prz->buffer->sig);
+		prz->buffer->sig = sig;
+		zap = true;
 	}
 
-	/* Rewind missing or invalid memory area. */
-	prz->buffer->sig = sig;
-	persistent_ram_zap(prz);
+	/* Reset missing, invalid, or single-use memory area. */
+	if (zap)
+		persistent_ram_zap(prz);
 
 	return 0;
 }
@@ -572,6 +593,12 @@ struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
 	if (ret)
 		goto err;
 
+	pr_debug("attached %s 0x%zx@0x%llx: %zu header, %zu data, %zu ecc (%d/%d)\n",
+		prz->label, prz->size, (unsigned long long)prz->paddr,
+		sizeof(*prz->buffer), prz->buffer_size,
+		prz->size - sizeof(*prz->buffer) - prz->buffer_size,
+		prz->ecc_info.ecc_size, prz->ecc_info.block_size);
+
 	return prz;
 err:
 	persistent_ram_free(prz);