Revert "pstore: Don't use semaphores in always-atomic-context code"

This reverts commit 86a926c3f0.

It breaks the abi and is not needed for Android devices so it can be
dropped.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I1583e40adde7173e3bd1283ea23feefe7c1e610c

drivers/firmware/efi/efi-pstore.c

@@ -266,7 +266,7 @@ static int efi_pstore_write(struct pstore_record *record)
 		efi_name[i] = name[i];
 
 	ret = efivar_entry_set_safe(efi_name, vendor, PSTORE_EFI_ATTRIBUTES,
-			      false, record->size, record->psi->buf);
+			      preemptible(), record->size, record->psi->buf);
 
 	if (record->reason == KMSG_DUMP_OOPS && try_module_get(THIS_MODULE))
 		if (!schedule_work(&efivar_work))

fs/pstore/platform.c

@@ -143,22 +143,21 @@ static void pstore_timer_kick(void)
 	mod_timer(&pstore_timer, jiffies + msecs_to_jiffies(pstore_update_ms));
 }
 
-static 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 spinning on
-	 * pstore_info::buf_lock.
-	 */
+	/* Emergency restart shouldn't be blocked. */
 	case KMSG_DUMP_EMERG:
 		return true;
 	default:
@@ -389,19 +388,21 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
-	unsigned long	flags = 0;
 	int		ret;
 
 	why = kmsg_dump_reason_str(reason);
 
-	if (pstore_cannot_block_path(reason)) {
-		if (!spin_trylock_irqsave(&psinfo->buf_lock, flags)) {
-			pr_err("dump skipped in %s path because of concurrent dump\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);
 	}
 
 	oopscount++;
@@ -463,7 +464,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		total += record.size;
 		part++;
 	}
-	spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+
+	up(&psinfo->buf_lock);
 }
 
 static struct kmsg_dumper pstore_dumper = {
@@ -589,7 +591,7 @@ int pstore_register(struct pstore_info *psi)
 		psi->write_user = pstore_write_user_compat;
 	psinfo = psi;
 	mutex_init(&psinfo->read_mutex);
-	spin_lock_init(&psinfo->buf_lock);
+	sema_init(&psinfo->buf_lock, 1);
 
 	if (psi->flags & PSTORE_FLAGS_DMESG)
 		allocate_buf_for_compression();

include/linux/pstore.h

@@ -14,7 +14,7 @@
 #include <linux/errno.h>
 #include <linux/kmsg_dump.h>
 #include <linux/mutex.h>
-#include <linux/spinlock.h>
+#include <linux/semaphore.h>
 #include <linux/time.h>
 #include <linux/types.h>
 
@@ -87,7 +87,7 @@ struct pstore_record {
  * @owner:	module which is responsible for this backend driver
  * @name:	name of the backend driver
  *
- * @buf_lock:	spinlock to serialize access to @buf
+ * @buf_lock:	semaphore to serialize access to @buf
  * @buf:	preallocated crash dump buffer
  * @bufsize:	size of @buf available for crash dump bytes (must match
  *		smallest number of bytes available for writing to a
@@ -178,7 +178,7 @@ struct pstore_info {
 	struct module	*owner;
 	const char	*name;
 
-	spinlock_t	buf_lock;
+	struct semaphore buf_lock;
 	char		*buf;
 	size_t		bufsize;