Re: [PATCH] mm/page-writeback: Consolidate wb_thresh bumping logic into __wb_calc_thresh

[Guenter Roeck]

On 1/14/25 05:19, Jan Kara wrote:
> On Mon 13-01-25 15:05:25, Guenter Roeck wrote:
> > Hi,
> >
> > On Thu, Nov 21, 2024 at 06:05:39PM +0800, Jim Zhao wrote:
> > > Address the feedback from "mm/page-writeback: raise wb_thresh to prevent
> > > write blocking with strictlimit"(39ac99852fca98ca44d52716d792dfaf24981f53).
> > > The wb_thresh bumping logic is scattered across wb_position_ratio,
> > > __wb_calc_thresh, and wb_update_dirty_ratelimit. For consistency,
> > > consolidate all wb_thresh bumping logic into __wb_calc_thresh.
> > >
> > > Reviewed-by: Jan Kara <jack@xxxxxxx>
> > > Signed-off-by: Jim Zhao <jimzhao.ai@xxxxxxxxx>
> >
> > This patch triggers a boot failure with one of my 'sheb' boot tests.
> > It is seen when trying to boot from flash (mtd). The log says
> >
> > ...
> > Starting network: 8139cp 0000:00:02.0 eth0: link down
> > udhcpc: started, v1.33.0
> > EXT2-fs (mtdblock3): error: ext2_check_folio: bad entry in directory #363: : directory entry across blocks - offset=0, inode=27393, rec_len=3072, name_len=2
> > udhcpc: sending discover
> > udhcpc: sending discover
> > udhcpc: sending discover
> > EXT2-fs (mtdblock3): error: ext2_check_folio: bad entry in directory #363: : directory entry across blocks - offset=0, inode=27393, rec_len=3072, name_len=2
>
> Thanks for report! Uh, I have to say I'm very confused by this. It is clear
> than when ext2 detects the directory corruption (we fail checking directory
> inode 363 which is likely /etc/init.d/), the boot fails in interesting
> ways. What is unclear is how the commit can possibly cause ext2 directory
> corruption.  If you didn't verify reverting the commit fixes the issue, I'd
> be suspecting bad bisection but that obviously isn't the case :-)
>
> Ext2 is storing directory data in the page cache so at least it uses the
> subsystem which the patch impacts but how writeback throttling can cause
> ext2 directory corruption is beyond me. BTW, do you recreate the root
> filesystem before each boot? How exactly?

I use pre-built root file systems. For sheb, they are at
https://github.com/groeck/linux-build-test/tree/master/rootfs/sheb

I don't think this is related to ext2 itself. Booting an ext2 image from
ata/ide drive works.

Guenter