[PATCH] UBIFS: Kernel oops on a read only mounted file system

[PATCH] UBIFS: Kernel oops on a read only mounted file system

[Daniel Fahlgren]

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Hi,

I have a system where the kernel is getting an oops a couple of seconds
after it has booted. It can also be provoked to happen earlier if I run
the command sync. The only ubifs file system on the machine is a read
only mounted root partition. The call trace is:

Call Trace:
[c7a57d50] [c00d3aa4] make_reservation+0xa0/0x434 (unreliable)
[c7a57db0] [c00d44c4] ubifs_jnl_write_inode+0x7c/0x248
[c7a57df0] [c00db898] ubifs_write_inode+0xd4/0x11c
[c7a57e10] [c009a1c8] __writeback_single_inode+0x424/0x42c
[c7a57e60] [c009a950] generic_sync_sb_inodes+0x444/0x56c
[c7a57ea0] [c009ab44] sync_inodes_sb+0xcc/0xe8
[c7a57ef0] [c009ac08] __sync_inodes+0xa8/0x12c
[c7a57f10] [c009aca8] sync_inodes+0x1c/0x50
[c7a57f20] [c009eae0] do_sync+0x24/0x84
[c7a57f30] [c009eb54] sys_sync+0x14/0x28
[c7a57f40] [c0010b10] ret_from_syscall+0x0/0x38
--- Exception: c01 at 0x10061d78

Neither the kernel nor the ubifs system is the latest, but the code in
ubifs_write_inode hasn't changed since 2008-something.

Looking at the list there is another similar report[1] but that isn't in
the same place. Attached is a patch that fixes the problem for me. To be
honest is my local version slightly different and is checking for
inode->i_sb->s_flags & MS_RDONLY and not c->ro_mount. I'm not sure if it
is in the correct place regarding locks, or if the check should be in
ubifs_jnl_write instead.

Best regards,
Daniel Fahlgren

1: http://lists.infradead.org/pipermail/linux-mtd/2011-April/034884.html

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diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 20403dc..be472d1 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -301,6 +301,9 @@ static int ubifs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	if (is_bad_inode(inode))
 		return 0;
 
+	if (c->ro_mount)
+		return 0;
+
 	mutex_lock(&ui->ui_mutex);
 	/*
 	 * Due to races between write-back forced by budgeting

Re: [PATCH] UBIFS: Kernel oops on a read only mounted file system

[Artem Bityutskiy]

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On Tue, 2011-12-13 at 08:53 +0100, Daniel Fahlgren wrote:
> Neither the kernel nor the ubifs system is the latest, but the code in
> ubifs_write_inode hasn't changed since 2008-something.
> 
> Looking at the list there is another similar report[1] but that isn't in
> the same place. Attached is a patch that fixes the problem for me. To be
> honest is my local version slightly different and is checking for
> inode->i_sb->s_flags & MS_RDONLY and not c->ro_mount. I'm not sure if it
> is in the correct place regarding locks, or if the check should be in
> ubifs_jnl_write instead.

I think this patch fixes the symptom, not the real cause. Most probably
it is a VFS bug in your kernel. If UBIFS is R/O, it should never have
any dirty inodes, so there should be nothing to write!

What is your kernel version? Can you enable generic UBIFS debugging and
collect the UBIFS prints and send them? Use ignore_loglevel kernel
argument when booting to make sure all UBIFS output goes to your
console, otherwise you'll not see them there and they will end up in the
ring buffer, and will probably overlap.

Thanks!

-- 
Best Regards,
Artem Bityutskiy

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