pstore: defer inserting OOPS entries into pstore

RFC-PATCH Luck, Tony 1 participant 1 message Aug 11, 2011 Pstore filesystem

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Luck, Tony

author reviewer

2011-08-11 22:14 UTC #0 lore raw

Life is simple for all the kernel terminating types of kmsg_dump call backs - pstore just saves the tail end of the console log. But for "oops" the situation is more complex - the kernel may carry on running (possibly for ever). So we'd like to make the logged copy of the oops appear in the pstore filesystem - so that the user has a handle to clear the entry from the persistent backing store (if we don't, the store may fill with "oops" entries (that are also safely stashed in /var/log/messages) leaving no space for real errors.

Current code calls pstore_mkfile() immediately. But this may not be safe. The oops could have happened with arbitrary locks held, or in interrupt or NMI context. So allocating memory and calling into generic filesystem code seems unwise.

This patch attempts to defer making the entry appear. At the time of the oops, we merely set a flag "pstore_new_entry" noting that a new entry has been added. A periodic timer checks once a minute to see if the flag is set - if so, it schedules a work queue to rescan the backing store and make all new entries appear in the pstore filesystem.

Signed-off-by Tony Luck <[email protected]>

Q: Is the "flag -> timer -> workqueue" indirection overkill? I was unsure whether it was safe to call schedule_work() while processing the OOPS.

---

fs/pstore/inode.c +36 -4

index 893b961..379a02d 100644
@@ -24,6 +24,7 @@
 #include <linux/highmem.h>
 #include <linux/time.h>
 #include <linux/init.h>
+#include <linux/list.h>
 #include <linux/string.h>
 #include <linux/mount.h>
 #include <linux/ramfs.h>

@@ -32,13 +33,18 @@
 #include <linux/magic.h>
 #include <linux/pstore.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/uaccess.h>
 
 #include "internal.h"
 
 #define	PSTORE_NAMELEN	64
 
+static DEFINE_SPINLOCK(allpstore_lock);
+static LIST_HEAD(allpstore);
+
 struct pstore_private {
+	struct list_head list;
 	struct pstore_info *psi;
 	enum pstore_type_id type;
 	u64	id;

@@ -81,8 +87,16 @@ static int pstore_unlink(struct inode *dir, struct dentry *dentry)
 
 static void pstore_evict_inode(struct inode *inode)
 {
+	struct pstore_private	*p = inode->i_private;
+	unsigned long		flags;
+
 	end_writeback(inode);
-	kfree(inode->i_private);
+	if (p) {
+		spin_lock_irqsave(&allpstore_lock, flags);
+		list_del(&p->list);
+		spin_unlock_irqrestore(&allpstore_lock, flags);
+		kfree(p);
+	}
 }
 
 static const struct inode_operations pstore_dir_inode_operations = {

@@ -182,9 +196,23 @@ int pstore_mkfile(enum pstore_type_id type, char *psname, u64 id,
 	struct dentry		*root = pstore_sb->s_root;
 	struct dentry		*dentry;
 	struct inode		*inode;
-	int			rc;
+	int			rc = 0;
 	char			name[PSTORE_NAMELEN];
-	struct pstore_private	*private;
+	struct pstore_private	*private, *pos;
+	unsigned long		flags;
+
+	spin_lock_irqsave(&allpstore_lock, flags);
+	list_for_each_entry(pos, &allpstore, list) {
+		if (pos->type == type &&
+		    pos->id == id &&
+		    pos->psi == psi) {
+			rc = -EEXIST;
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&allpstore_lock, flags);
+	if (rc)
+		return rc;
 
 	rc = -ENOMEM;
 	inode = pstore_get_inode(pstore_sb, root->d_inode, S_IFREG | 0444, 0);

@@ -229,6 +257,10 @@ int pstore_mkfile(enum pstore_type_id type, char *psname, u64 id,
 
 	d_add(dentry, inode);
 
+	spin_lock_irqsave(&allpstore_lock, flags);
+	list_add(&private->list, &allpstore);
+	spin_unlock_irqrestore(&allpstore_lock, flags);
+
 	mutex_unlock(&root->d_inode->i_mutex);
 
 	return 0;

@@ -277,7 +309,7 @@ int pstore_fill_super(struct super_block *sb, void *data, int silent)
 		goto fail;
 	}
 
-	pstore_get_records();
+	pstore_get_records(0);
 
 	return 0;
 fail:

fs/pstore/internal.h +1 -1

index 611c1b3..3bde461 100644
@@ -1,5 +1,5 @@
 extern void	pstore_set_kmsg_bytes(int);
-extern void	pstore_get_records(void);
+extern void	pstore_get_records(int);
 extern int	pstore_mkfile(enum pstore_type_id, char *psname, u64 id,
 			      char *data, size_t size,
 			      struct timespec time, struct pstore_info *psi);

fs/pstore/platform.c +45 -9

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