* [PATCH] ext2: do not sleep in ext2_error()
@ 2021-09-03 9:05 Dan Carpenter
2021-09-03 12:48 ` Theodore Ts'o
0 siblings, 1 reply; 4+ messages in thread
From: Dan Carpenter @ 2021-09-03 9:05 UTC (permalink / raw)
To: Jan Kara; +Cc: linux-ext4, linux-kernel, kernel-janitors
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 <dan.carpenter@oracle.com>
---
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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] ext2: do not sleep in ext2_error()
2021-09-03 9:05 [PATCH] ext2: do not sleep in ext2_error() Dan Carpenter
@ 2021-09-03 12:48 ` Theodore Ts'o
2021-09-03 13:09 ` Dan Carpenter
2021-09-16 9:48 ` Jan Kara
0 siblings, 2 replies; 4+ messages in thread
From: Theodore Ts'o @ 2021-09-03 12:48 UTC (permalink / raw)
To: Dan Carpenter; +Cc: Jan Kara, linux-ext4, linux-kernel, kernel-janitors
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 <dan.carpenter@oracle.com>
> ---
> 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().
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ext2: do not sleep in ext2_error()
2021-09-03 12:48 ` Theodore Ts'o
@ 2021-09-03 13:09 ` Dan Carpenter
2021-09-16 9:48 ` Jan Kara
1 sibling, 0 replies; 4+ messages in thread
From: Dan Carpenter @ 2021-09-03 13:09 UTC (permalink / raw)
To: Theodore Ts'o; +Cc: Jan Kara, linux-ext4, linux-kernel, kernel-janitors
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:
> > 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 <dan.carpenter@oracle.com>
> > ---
> > 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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ext2: do not sleep in ext2_error()
2021-09-03 12:48 ` Theodore Ts'o
2021-09-03 13:09 ` Dan Carpenter
@ 2021-09-16 9:48 ` Jan Kara
1 sibling, 0 replies; 4+ messages in thread
From: Jan Kara @ 2021-09-16 9:48 UTC (permalink / raw)
To: Theodore Ts'o
Cc: Dan Carpenter, Jan Kara, linux-ext4, linux-kernel, kernel-janitors
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:
> > 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 <dan.carpenter@oracle.com>
> > ---
> > 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 <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-09-03 12:48 ` Theodore Ts'o
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