Re: [f2fs-dev] F2fs panic | update_sit_entry() | no free segment | se invalid

[Chao Yu <yuchao0@huawei.com>]

Hi 王矛，

On 2020/2/16 19:39, 王矛 wrote:
> *So the problem is:*
> 
> 1. in new_curseg(), if the segno allocated is invalid(no free segment, max segno
> is returned).
> 
> F2fs should do something to indicate this exception.
> 
> 2. otherwise, we may hit the f2fs panic(se invalid).
> 
> Maybe we should do sanity check in update_sit_entry() to see if segno is really
> out of range and caused this panic.

I'm afraid it's too late to handle such error in update_sit_entry(), since we
expect all procedures in do_write_page() will be successful, it's a little hard
to handle such error in that context.

So the problem here is why we can not find any free segments w/ LFS allocation,
because in case of lack of free segments (check via has_not_enough_free_secs()),
f2fs will force to trigger f2fs_gc() to recycle free sections.

I doubt there may be some corner case we haven't considered, result all free
segments (including reserved free segments) was exhausted by data/node writes
when last checkpoint is triggered during umount.

If this issue can be reproduced (during umount, free_segments() <
reserved_segments()), we can add some logs to see why f2fs_balance_fs() fail to
recycle enough free segments previously.

Thanks,

> 
> 
> Thanks,
> Mao
> 
> 
> 
>  
> 


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