[PATCH] ext2: do not sleep in ext2_error()

No one expects error logging functions to sleep so sometimes they are
called with spinlocks held.  In this case the problematic call tree is:

ext2_statfs() <- disables preempt
-> ext2_count_free_inodes()
   -> ext2_get_group_desc()
      -> ext2_error()

Signed-off-by: Dan Carpenter <redacted>
---
This is just from static analysis.  NOT TESTED!

Probably a safer fix would be to just call pr_err() instead of
ext2_error() in ext2_get_group_desc().  I can send that fix instead if
people want.

 fs/ext2/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index d8d580b609ba..ba345ab860f0 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c

@@ -59,7 +59,7 @@ void ext2_error(struct super_block *sb, const char *function,
 		sbi->s_mount_state |= EXT2_ERROR_FS;
 		es->s_state |= cpu_to_le16(EXT2_ERROR_FS);
 		spin_unlock(&sbi->s_lock);
-		ext2_sync_super(sb, es, 1);
+		ext2_sync_super(sb, es, 0);
 	}
 
 	va_start(args, fmt);

-- 
2.20.1

On Fri, Sep 03, 2021 at 12:05:38PM +0300, Dan Carpenter wrote:

No one expects error logging functions to sleep so sometimes they are
called with spinlocks held.  In this case the problematic call tree is:

ext2_statfs() <- disables preempt
-> ext2_count_free_inodes()
   -> ext2_get_group_desc()
      -> ext2_error()

Signed-off-by: Dan Carpenter <redacted>
---
This is just from static analysis.  NOT TESTED!

Probably a safer fix would be to just call pr_err() instead of
ext2_error() in ext2_get_group_desc().  I can send that fix instead if
people want.

Looking at both of the ext2_error() calls in ext2_get_group_desc(),
those are really more in the way of assertions rather than warning of
an on-disk corruption issue.  The second "group descriptor not loaded"
should never happen, and the "block_group >= groups_count" should have
been caught via an invalid block number or check by the caller (or an
outright code bug in say ext2_statfs().

So I suspect both of those would be more usefule as a WARN() rather
than a call to ext2_error(), since stack trace would actually provide
more useful data to root causing the issue.  Jan, what do you think?

     	    	    	 	 - Ted

P.S.  The same analysis applies for ext4_get_group_desc(), BTW.  We
don't take a lock in ext4_statfs() so trying to take a lock while
sleeping is not an issue.

For both ext2 and ext4, the caller is not supposed to holding spin
locks when it calls ext[24]_error().  In cases where it is absolutely
not avoidable, special measures are required --- see for example
__ext4_grp_locked_error().

On Fri, Sep 03, 2021 at 08:48:38AM -0400, Theodore Ts'o wrote:

On Fri, Sep 03, 2021 at 12:05:38PM +0300, Dan Carpenter wrote:

quoted

No one expects error logging functions to sleep so sometimes they are
called with spinlocks held.  In this case the problematic call tree is:

ext2_statfs() <- disables preempt
-> ext2_count_free_inodes()
   -> ext2_get_group_desc()
      -> ext2_error()

Signed-off-by: Dan Carpenter <redacted>
---
This is just from static analysis.  NOT TESTED!

Probably a safer fix would be to just call pr_err() instead of
ext2_error() in ext2_get_group_desc().  I can send that fix instead if
people want.

Looking at both of the ext2_error() calls in ext2_get_group_desc(),
those are really more in the way of assertions rather than warning of
an on-disk corruption issue.  The second "group descriptor not loaded"
should never happen, and the "block_group >= groups_count" should have
been caught via an invalid block number or check by the caller (or an
outright code bug in say ext2_statfs().

So I suspect both of those would be more usefule as a WARN() rather
than a call to ext2_error(), since stack trace would actually provide
more useful data to root causing the issue.  Jan, what do you think?

     	    	    	 	 - Ted

Thanks Ted,

I'll resend with the WARN() change.

regards,
dan carpenter

On Fri 03-09-21 08:48:38, Theodore Ts'o wrote:

On Fri, Sep 03, 2021 at 12:05:38PM +0300, Dan Carpenter wrote:

quoted

No one expects error logging functions to sleep so sometimes they are
called with spinlocks held.  In this case the problematic call tree is:

ext2_statfs() <- disables preempt
-> ext2_count_free_inodes()
   -> ext2_get_group_desc()
      -> ext2_error()

Signed-off-by: Dan Carpenter <redacted>
---
This is just from static analysis.  NOT TESTED!

Probably a safer fix would be to just call pr_err() instead of
ext2_error() in ext2_get_group_desc().  I can send that fix instead if
people want.

Looking at both of the ext2_error() calls in ext2_get_group_desc(),
those are really more in the way of assertions rather than warning of
an on-disk corruption issue.  The second "group descriptor not loaded"
should never happen, and the "block_group >= groups_count" should have
been caught via an invalid block number or check by the caller (or an
outright code bug in say ext2_statfs().

So I suspect both of those would be more usefule as a WARN() rather
than a call to ext2_error(), since stack trace would actually provide
more useful data to root causing the issue.  Jan, what do you think?

Yes, I agree. Definitely better than not flushing error on other
ext2_error() calls. BTW, Dan, I don't see a patch with WARN() in my inbox.
Did it get lost somewhere?

								Honza

-- 
Jan Kara [off-list ref]
SUSE Labs, CR