Re: [PATCH 2/2] ext4: correct the judgment of BUG in ext4_mb_normalize_request

[Baokun Li]

在 2022/5/24 4:08, Ritesh Harjani 写道:
> On 22/05/21 09:42PM, Baokun Li wrote:
> > When either of the "start + size <= ac->ac_o_ex.fe_logical" or
> > "start > ac->ac_o_ex.fe_logical" conditions is met, it indicates
> > that the fe_logical is not in the allocated range.
> Sounds about right to me based on the logic in ext4_mb_use_inode_pa().
> We try to allocate/preallocate such that ac->ac_o_ex.fe_logical should fall
> within the preallocated range. So if our start or start + size doesn't include
> fe_logical then it is a bug in the ext4_mb_normalize_request() logic.
Yes, exactly.
> But should we be so harsh to hit a bug_on() or make it warn_on()?
I don't think hit a bug_on() is a problem. BUG_ON is not triggered here 
and will be triggered later.
> Also did you run any fs tests with this change.
Yes, I ran xfstests on ext3 and ext4 and found no problems.
> Since it looks like this
> logic existed since mballoc was introduced.
Yes, on our coverage report, those lines of code never seem to get there.

> > In this case, it should be bug_ON.
> >
> > Fixes: dfe076c106f6 ("ext4: get rid of code duplication")
> No, there is no issue with this patch. It correctly just removes the duplicate
> logic.
Okay, I'm going to remove this tag.
> > Signed-off-by: Baokun Li<libaokun1@xxxxxxxxxx>
> > ---
> >   fs/ext4/mballoc.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 32410b79b664..d0fb57970648 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -4190,7 +4190,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
> >   	}
> >   	rcu_read_unlock();
> >
> > -	if (start + size <= ac->ac_o_ex.fe_logical &&
> > +	if (start + size <= ac->ac_o_ex.fe_logical ||
> >   			start > ac->ac_o_ex.fe_logical) {
> >   		ext4_msg(ac->ac_sb, KERN_ERR,
> >   			 "start %lu, size %lu, fe_logical %lu",
> > --
> > 2.31.1
> .

--
With Best Regards,
Baokun Li