JFFS2 deadlock with alloc_sem

[Dave Kleikamp]

On Fri, 2007-07-27 at 11:38 +0800, ye janboe wrote:
> Does this make fsync system call failed to cause a risk of loss data?

Could be.  It looks like I wasn't careful about considering all the
callers of jffs2_garbage_collect_pass().  I assume the problem is when
it is called from jffs2_flush_wbuf_gc().

> I posted my fix base on your patch, please review it.
> 
> Thanks
> 
> --- gc.c@@/main/fl71_main/a22116_jffs2_sync_debug/0     2007-07-24
> 17:02:26.746154000 +0800
> +++ gc.c@@/main/fl71_main/a22116_jffs2_sync_debug/2     2007-07-24
> 17:39:35.000000000 +0800
> @@ -1299,7 +1299,10 @@ static int jffs2_garbage_collect_dnode(s
>         if (IS_ERR(pg_ptr)) {
>                 if ( PTR_ERR(pg_ptr) == -EBUSY ) {
>                         printk(KERN_WARNING "jffs2_gc_fetch_page() rc
> -EBUSY. Deadlock avoided.\n" );
> -                       return 0;
> +                       if (current->flags & PF_SYNCWRITE)
> +                               return -EBUSY;
> +                       else
> +                               return 0;
>                 } else {
>                         printk(KERN_WARNING "jffs2_gc_fetch_page() rc
> %ld\n", PTR_ERR(pg_ptr));
>                         return PTR_ERR(pg_ptr);

That is probably okay, but I think it is getting more complicated than
it needs to be. 

What if we let jffs2_garbage_collect_dnode() return -EBUSY all the time,
and let the callers that don't care ignore it?

How's this look?

diff -Nurp linux.orig/fs/jffs2/gc.c linux/fs/jffs2/gc.c
--- linux.orig/fs/jffs2/gc.c	2007-07-27 08:32:36.000000000 -0500
+++ linux/fs/jffs2/gc.c	2007-07-27 08:33:59.000000000 -0500
@@ -1221,13 +1221,8 @@ static int jffs2_garbage_collect_dnode(s
 	pg_ptr = jffs2_gc_fetch_page(c, f, start, &pg);
 
 	if (IS_ERR(pg_ptr)) {
-		if ( PTR_ERR(pg_ptr) == -EBUSY ) {
-			printk(KERN_WARNING "jffs2_gc_fetch_page() rc -EBUSY. Deadlock avoided.\n" );
-			return 0;
-		} else {
-			printk(KERN_WARNING "jffs2_gc_fetch_page() rc %ld\n", PTR_ERR(pg_ptr));
-			return PTR_ERR(pg_ptr);
-		}
+		printk(KERN_WARNING "jffs2_gc_fetch_page() rc %ld\n", PTR_ERR(pg_ptr));
+		return PTR_ERR(pg_ptr);
 	}
 
 	offset = start;
diff -Nurp linux.orig/fs/jffs2/nodemgmt.c linux/fs/jffs2/nodemgmt.c
--- linux.orig/fs/jffs2/nodemgmt.c	2007-07-27 08:32:25.000000000 -0500
+++ linux/fs/jffs2/nodemgmt.c	2007-07-27 08:35:46.000000000 -0500
@@ -117,7 +117,7 @@ int jffs2_reserve_space(struct jffs2_sb_
 			spin_unlock(&c->erase_completion_lock);
 
 			ret = jffs2_garbage_collect_pass(c);
-			if (ret)
+			if (ret && (ret != -EBUSY))
 				return ret;
 
 			cond_resched();

-- 
David Kleikamp
IBM Linux Technology Center