Re: [BUG REPORT] shrink_dcache_parent() loops indefinitely on a next-20240102 kernel

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Jan 18, 2024 at 10:59:06AM +0530, Chandan Babu R wrote:
> On Thu, Jan 04, 2024 at 06:40:43 PM +0530, Chandan Babu R wrote:
> > On Wed, Jan 03, 2024 at 08:34:20 PM -0800, Darrick J. Wong wrote:
> >> On Wed, Jan 03, 2024 at 12:12:12PM +0530, Chandan Babu R wrote:
> >>> Hi,
> >>> 
> >>> Executing fstests' recoveryloop test group on XFS on a next-20240102 kernel
> >>> sometimes causes the following hung task report to be printed on the console,
> >>> 
> 
> Meanwhile, I have executed some more experiments.
> 
> The bug can be recreated on a next-20240102 kernel by executing either
> generic/388 or generic/475 for a maximum of 10 iterations. I tried to do a git
> bisect based on this observation i.e. I would mark a commit as 'good' if the
> bug does not get recreated within 10 iterations. This led to the following git
> bisect log,

> # bad: [119dcc73a9c2df0da002054cdb2296cb32b7cb93] Merge branches 'work.dcache-misc' and 'work.dcache2' into work.dcache
> git bisect bad 119dcc73a9c2df0da002054cdb2296cb32b7cb93
> # good: [6367b491c17a34b28aece294bddfda1a36ec0377] retain_dentry(): introduce a trimmed-down lockless variant
> git bisect good 57851607326a2beef21e67f83f4f53a90df8445a
> # good: [ef69f0506d8f3a250ac5baa96746e17ae22c67b5] __d_unalias() doesn't use inode argument

Lovely...  Could you try to do the following:

bisect from 6.7-rc1 to work.dcache-misc; for each of those revisions
	git worktree add ../test HEAD
	cd ../test
	git merge work.dcache2
	build
	test the result
	cd -
	git worktree remove -f ../test
	git bisect {good,bad} accordingly