jffs2: avoid soft-lockup in jffs2_reserve_space_gc()

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=13b546d96207c131eeae15dc7b26c6e7d0f1cad7
Commit:     13b546d96207c131eeae15dc7b26c6e7d0f1cad7
Parent:     3ead9578443b66ddb3d50ed4f53af8a0c0298ec5
Author:     Li Zefan <lizefan at huawei.com>
AuthorDate: Wed Feb 12 12:44:56 2014 -0800
Committer:  Brian Norris <computersforpeace at gmail.com>
CommitDate: Mon Mar 10 22:42:28 2014 -0700

    jffs2: avoid soft-lockup in jffs2_reserve_space_gc()
    
    We triggered soft-lockup under stress test on 2.6.34 kernel.
    
    BUG: soft lockup - CPU#1 stuck for 60009ms! [lockf2.test:14488]
    ...
    [<bf09a4d4>] (jffs2_do_reserve_space+0x420/0x440 [jffs2])
    [<bf09a528>] (jffs2_reserve_space_gc+0x34/0x78 [jffs2])
    [<bf0a1350>] (jffs2_garbage_collect_dnode.isra.3+0x264/0x478 [jffs2])
    [<bf0a2078>] (jffs2_garbage_collect_pass+0x9c0/0xe4c [jffs2])
    [<bf09a670>] (jffs2_reserve_space+0x104/0x2a8 [jffs2])
    [<bf09dc48>] (jffs2_write_inode_range+0x5c/0x4d4 [jffs2])
    [<bf097d8c>] (jffs2_write_end+0x198/0x2c0 [jffs2])
    [<c00e00a4>] (generic_file_buffered_write+0x158/0x200)
    [<c00e14f4>] (__generic_file_aio_write+0x3a4/0x414)
    [<c00e15c0>] (generic_file_aio_write+0x5c/0xbc)
    [<c012334c>] (do_sync_write+0x98/0xd4)
    [<c0123a84>] (vfs_write+0xa8/0x150)
    [<c0123d74>] (sys_write+0x3c/0xc0)]
    
    Fix this by adding a cond_resched() in the while loop.
    
    [akpm at linux-foundation.org: don't initialize `ret']
    Signed-off-by: Li Zefan <lizefan at huawei.com>
    Cc: David Woodhouse <dwmw2 at infradead.org>
    Cc: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>
    Cc: <stable at vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
 fs/jffs2/nodemgmt.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/jffs2/nodemgmt.c b/fs/jffs2/nodemgmt.c
index bbae5b1..b6bd4af 100644
--- a/fs/jffs2/nodemgmt.c
+++ b/fs/jffs2/nodemgmt.c
@@ -212,20 +212,25 @@ out:
 int jffs2_reserve_space_gc(struct jffs2_sb_info *c, uint32_t minsize,
 			   uint32_t *len, uint32_t sumsize)
 {
-	int ret = -EAGAIN;
+	int ret;
 	minsize = PAD(minsize);
 
 	jffs2_dbg(1, "%s(): Requested 0x%x bytes\n", __func__, minsize);
 
-	spin_lock(&c->erase_completion_lock);
-	while(ret == -EAGAIN) {
+	while (true) {
+		spin_lock(&c->erase_completion_lock);
 		ret = jffs2_do_reserve_space(c, minsize, len, sumsize);
 		if (ret) {
 			jffs2_dbg(1, "%s(): looping, ret is %d\n",
 				  __func__, ret);
 		}
+		spin_unlock(&c->erase_completion_lock);
+
+		if (ret == -EAGAIN)
+			cond_resched();
+		else
+			break;
 	}
-	spin_unlock(&c->erase_completion_lock);
 	if (!ret)
 		ret = jffs2_prealloc_raw_node_refs(c, c->nextblock, 1);