Re: ffs_truncate3 panics

On Wed, Aug 08, 2018 at 12:30:54PM +0000, Rick Macklem wrote:
> Konstantin Belousov wrote:
> >On Tue, Aug 07, 2018 at 12:28:33PM +0000, Rick Macklem wrote:
> >> Hi,
> >>
> >> During testing of the pNFS server I get an ffs_truncate3 panic every once in a while.
> >> A few things that might be relevant:
> >> - Seems to happen more often when soft update journaling is enabled, but will
> >>   happen when it is disabled.
> >> - Normally happens when a fairly large subtree of the file system is being removed.
> - Oh, and this is an old i386 with 256Mbytes (not one of them new fangled computers,
>    where memory is in Gbytes;-)
> 
> >>
> >> These file systems are a bit odd, since all the regular files in them are empty but
> >> have extended attributes that are accessed during the subtree removal. (The
> >> extended attributes tell the server where the data files are.)
> >>
> >> I replaced the panic() with a printf() and every time the printf() happens...
> >> bo->bo_dirty.bv_cnt == 0 and bo->bo_clean.bv_cnt == 1.
> >> After one of these printf()s, the system continues to run ok. When the file
> >> system is fsck'd after this has occurred, it passes fine and I haven't seen and
> >> indication of file system corruption after running with this file system for
> >> quite a while after the printf()s first occurred.
> >The lack of corruption is, most likely, because the files are removed.
> >Would the files truncated to zero length and then extended, I am almost
> >sure that a corruption occur.
> >
> >Can you print the only buffer on the clean queue when the panic occur ?
> ffst3 vtyp=1 bodirty=0 boclean=1
> buf at 0x428a110
> b_flags = 0x20001020<vmio,reuse,cache>, b_xflags=0x2<clean>, b_vflags=0x0
> b_error = 0, b_bufsize = 4096, b_bcount = 4096, b_resid = 0
> b_bufobj = (0xfd8ba94), b_data = 0x5170000, b_blkno = -1, b_lblkno = -1, b_dep = 0
> b_kvabase = 0x5170000, b_kvasize = 32768
So the buffer was indeed for extended attrs, and never written to the disk.
I am quite interested what was the inode content prior to the truncation,
esp. the di_extsize.

Could you try to formulate a way to reproduce the panic so that Peter
can recreate it, please ?

> 
> >Also, it is interesting to know the initial length of the file.
> Since they are regular files, they are 0 length. (Just inodes with extended attributes.)
> 
> >>
> >> Since the panic() only occurs when "options INVARIANTS" is enabled and I don't
> >> see evidence of file system corruption, I'm wondering if this panic() is valid and
> >> needed?
> 
> rick