[OpenWrt-Devel] [PATCH] jffs2: Fix use of uninitialized delayed_work, lockdep breakage

[Daniel Santos]

I've sent this one upstream.  This patch is critical if you want to run
with "prove lock correctness" (lockdep) and you happen to have certain
mtd devices.  The misuse of the uninitialized object is undefined
behaviour, but being zeroed it does not appear to have actually broken
anything other than the lockdep engine.

Signed-off-by: Daniel Santos <daniel.santos at pobox.com>
---
 ...se-of-uninitialized-delayed_work-lockdep-.patch | 64 ++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 target/linux/generic/pending-4.14/142-jffs2-Fix-use-of-uninitialized-delayed_work-lockdep-.patch

diff --git a/target/linux/generic/pending-4.14/142-jffs2-Fix-use-of-uninitialized-delayed_work-lockdep-.patch b/target/linux/generic/pending-4.14/142-jffs2-Fix-use-of-uninitialized-delayed_work-lockdep-.patch
new file mode 100644
index 0000000000..5b2184f340
--- /dev/null
+++ b/target/linux/generic/pending-4.14/142-jffs2-Fix-use-of-uninitialized-delayed_work-lockdep-.patch
@@ -0,0 +1,64 @@
+From 1d9ab2b7c27a10acfa437c561f276d52d563e058 Mon Sep 17 00:00:00 2001
+From: Daniel Santos <daniel.santos at pobox.com>
+Date: Fri, 19 Oct 2018 01:50:20 -0500
+Subject: jffs2: Fix use of uninitialized delayed_work, lockdep breakage
+
+jffs2_sync_fs makes the assumption that if CONFIG_JFFS2_FS_WRITEBUFFER
+is defined then a write buffer is available and has been initialized.
+However, this does is not the case when the mtd device has no
+out-of-band buffer:
+
+int jffs2_nand_flash_setup(struct jffs2_sb_info *c)
+{
+        if (!c->mtd->oobsize)
+                return 0;
+...
+
+The resulting call to cancel_delayed_work_sync passing a uninitialized
+(but zeroed) delayed_work struct forces lockdep to become disabled.
+
+[   90.050639] overlayfs: upper fs does not support tmpfile.
+[   90.652264] INFO: trying to register non-static key.
+[   90.662171] the code is fine but needs lockdep annotation.
+[   90.673090] turning off the locking correctness validator.
+[   90.684021] CPU: 0 PID: 1762 Comm: mount_root Not tainted 4.14.63 #0
+[   90.696672] Stack : 00000000 00000000 80d8f6a2 00000038 805f0000 80444600 8fe364f4 805dfbe7
+[   90.713349]         80563a30 000006e2 8068370c 00000001 00000000 00000001 8e2fdc48 ffffffff
+[   90.730020]         00000000 00000000 80d90000 00000000 00000106 00000000 6465746e 312e3420
+[   90.746690]         6b636f6c 03bf0000 f8000000 20676e69 00000000 80000000 00000000 8e2c2a90
+[   90.763362]         80d90000 00000001 00000000 8e2c2a90 00000003 80260dc0 08052098 80680000
+[   90.780033]         ...
+[   90.784902] Call Trace:
+[   90.789793] [<8000f0d8>] show_stack+0xb8/0x148
+[   90.798659] [<8005a000>] register_lock_class+0x270/0x55c
+[   90.809247] [<8005cb64>] __lock_acquire+0x13c/0xf7c
+[   90.818964] [<8005e314>] lock_acquire+0x194/0x1dc
+[   90.828345] [<8003f27c>] flush_work+0x200/0x24c
+[   90.837374] [<80041dfc>] __cancel_work_timer+0x158/0x210
+[   90.847958] [<801a8770>] jffs2_sync_fs+0x20/0x54
+[   90.857173] [<80125cf4>] iterate_supers+0xf4/0x120
+[   90.866729] [<80158fc4>] sys_sync+0x44/0x9c
+[   90.875067] [<80014424>] syscall_common+0x34/0x58
+
+Signed-off-by: Daniel Santos <daniel.santos at pobox.com>
+---
+ fs/jffs2/super.c | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
+index 793ad30970ff..cae4ecda3c50 100644
+--- a/fs/jffs2/super.c
++++ b/fs/jffs2/super.c
+@@ -101,7 +101,8 @@ static int jffs2_sync_fs(struct super_block *sb, int wait)
+ 	struct jffs2_sb_info *c = JFFS2_SB_INFO(sb);
+ 
+ #ifdef CONFIG_JFFS2_FS_WRITEBUFFER
+-	cancel_delayed_work_sync(&c->wbuf_dwork);
++	if (jffs2_is_writebuffered(c))
++		cancel_delayed_work_sync(&c->wbuf_dwork);
+ #endif
+ 
+ 	mutex_lock(&c->alloc_sem);
+-- 
+2.16.4
+
-- 
2.16.4


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