anolis: pstore: replace might_sleep rcu_read_lock with mutex

ANBZ: #4274

Pstore currently use rcu_read_lock and would result
in might_sleep. Replace rcu_read_lock with mutex when
there is no might_sleep in context.

Signed-off-by: Yuanhe Shu <xiangzao@linux.alibaba.com>
Reviewed-by: Xunlei Pang <xlpang@linux.alibaba.com>
Link: https://gitee.com/anolis/cloud-kernel/pulls/1452

fs/pstore/inode.c

@@ -510,12 +510,12 @@ static int pstore_fill_super(struct super_block *sb, void *data, int silent)
 	pstore_sb = sb;
 	mutex_unlock(&pstore_sb_lock);
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &psback->list_entry, list) {
+	mutex_lock(&psback_lock);
+	list_for_each_entry(entry, &psback->list_entry, list) {
 		pstore_mksubdir(entry->psi);
 		pstore_get_records(entry->psi, entry->index, 0);
 	}
-	rcu_read_unlock();
+	mutex_unlock(&psback_lock);
 
 	psback->fs_ready = true;
 

fs/pstore/platform.c

@@ -74,7 +74,7 @@ static DECLARE_WORK(pstore_work, pstore_dowork);
  * pstore_register(), pstore_unregister(), and
  * the filesystem mount/unmount routines.
  */
-static DEFINE_MUTEX(psback_lock);
+DEFINE_MUTEX(psback_lock);
 struct pstore_backends *psback;
 
 static char *compress =
@@ -605,15 +605,13 @@ int pstore_register(struct pstore_info *psi)
 			mutex_unlock(&psback_lock);
 			return -EBUSY;
 		}
-		rcu_read_lock();
-		list_for_each_entry_rcu(entry, &psback->list_entry, list) {
+		list_for_each_entry(entry, &psback->list_entry, list) {
 			if (strcmp(entry->psi->name, psi->name) == 0) {
 				pr_warn("ignoring unexpected backend '%s'\n", psi->name);
 				mutex_unlock(&psback_lock);
 				return -EPERM;
 			}
 		}
-		rcu_read_unlock();
 	}
 
 	if (!psback) {
@@ -629,7 +627,6 @@ int pstore_register(struct pstore_info *psi)
 	pslist->psi = psi;
 	pslist->index = ffz(psback->flag);
 	INIT_LIST_HEAD(&pslist->list);
-	list_add_rcu(&pslist->list, &psback->list_entry);
 	psback->flag |= (1 << pslist->index);
 
 	mutex_init(&psi->read_mutex);
@@ -659,6 +656,8 @@ int pstore_register(struct pstore_info *psi)
 	/* Start watching for new records, if desired. */
 	pstore_timer_kick();
 
+	list_add_rcu(&pslist->list, &psback->list_entry);
+
 	pr_info("Registered %s as persistent store backend\n", psi->name);
 
 	mutex_unlock(&psback_lock);
@@ -694,17 +693,16 @@ void pstore_unregister(struct pstore_info *psi)
 	/* Remove all backend records from filesystem tree. */
 	pstore_put_backend_records(psi);
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &psback->list_entry, list) {
+	list_for_each_entry(entry, &psback->list_entry, list) {
 		if (entry->psi == psi) {
-			free_buf_for_compression(entry->index);
 			list_del_rcu(&entry->list);
 			psback->flag ^= 1 << entry->index;
+			synchronize_rcu();
+			free_buf_for_compression(entry->index);
 			kfree(entry);
 			break;
 		}
 	}
-	rcu_read_unlock();
 
 	if (psback->flag == PSOTRE_LIST_EMPTY) {
 		kfree(psback);
@@ -840,10 +838,10 @@ static void pstore_dowork(struct work_struct *work)
 {
 	struct pstore_info_list *entry;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &psback->list_entry, list)
+	mutex_lock(&psback_lock);
+	list_for_each_entry(entry, &psback->list_entry, list)
 		pstore_get_records(entry->psi, entry->index, 1);
-	rcu_read_unlock();
+	mutex_unlock(&psback_lock);
 }
 
 static void pstore_timefunc(struct timer_list *unused)
@@ -886,18 +884,18 @@ static int __init pstore_init(void)
 	 * initialize compression because crypto was not ready. If so,
 	 * initialize compression now.
 	 */
-	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &psback->list_entry, list)
+	mutex_lock(&psback_lock);
+	list_for_each_entry(entry, &psback->list_entry, list)
 		allocate_buf_for_compression(entry->psi, entry->index);
-	rcu_read_unlock();
+	mutex_unlock(&psback_lock);
 
 	ret = pstore_init_fs();
 
 	if (ret) {
-		rcu_read_lock();
-		list_for_each_entry_rcu(entry, &psback->list_entry, list)
+		mutex_lock(&psback_lock);
+		list_for_each_entry(entry, &psback->list_entry, list)
 			free_buf_for_compression(entry->index);
-		rcu_read_unlock();
+		mutex_unlock(&psback_lock);
 	}
 
 	return ret;

fs/pstore/pmsg.c

@@ -40,15 +40,15 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf,
 	int ret;
 	struct pstore_info_list *entry;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(entry, &psback->list_entry, list) {
+	mutex_lock(&psback_lock);
+	list_for_each_entry(entry, &psback->list_entry, list) {
 		if (entry->psi->flags & PSTORE_FLAGS_PMSG) {
 			int _ret = do_write_pmsg(file, buf, count, ppos, entry->psi);
 
 			ret = ret > _ret ? ret : _ret;
 		}
 	}
-	rcu_read_unlock();
+	mutex_unlock(&psback_lock);
 
 	return ret;
 }

fs/pstore/ttyprobe.c

@@ -13,7 +13,6 @@
 #include <linux/tty_driver.h>
 #include "internal.h"
 
-static DEFINE_MUTEX(ttymsg_lock);
 DEFINE_STATIC_KEY_FALSE(ttyprobe_key);
 
 #define TTYPROBE_NAME "ttyprobe"
@@ -36,10 +35,8 @@ static void do_write_ttymsg(const unsigned char *buf, int count,
 	newline.size = strlen(lbreak);
 	newline.buf = lbreak;
 
-	mutex_lock(&ttymsg_lock);
 	psinfo->write(&record);
 	psinfo->write(&newline);
-	mutex_unlock(&ttymsg_lock);
 }
 
 void pstore_register_ttyprobe(void)

include/linux/pstore.h

@@ -236,6 +236,7 @@ struct pstore_backends {
 
 extern int pstore_register(struct pstore_info *);
 extern void pstore_unregister(struct pstore_info *);
+extern struct mutex psback_lock;
 
 struct pstore_ftrace_record {
 	unsigned long ip;