linux-kernel - debugging rmmod failures

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Message-ID: <CAH2r5mve4HKpPOwFuE5+r26xJ7f--M5+wC=kY0km9-T2WGak2A@mail.gmail.com>
Date:   Fri, 16 Sep 2022 15:13:52 -0500
From:   Steve French <smfrench@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: debugging rmmod failures

Any suggestions on how to debug why rmmod fails with EBUSY?

I was trying to debug a problem where rmmod fails during an xfstest
run but couldn't find useful information on how to get ideas 'why'
rmmod is failing (in this case with EBUSY) and I could only find two
places where EBUSY would plausibly be returned but don't see the
pr_debug message in the log (e.g. "already dying") that I would expect
to get in those cases.

It also fails in this test scenario (which takes a while to reproduce
so isn't trivial to repro) with EBUSY when doing "rmmod --verbose
--force"  and the --verbose didn't display any additional info.

I also tried "trace-cmd record -e *module*" which showed it (one call)
returning 0xFFFFFFF0 but nothing useful that I could see.

Any ideas on how to debug *why* an rmmod fails?
-- 
Thanks,

Steve