On Wed, Oct 27, 2021 at 01:57:40PM +0200, Miroslav Benes wrote:

On Tue, 26 Oct 2021, Luis Chamberlain wrote:

quoted

On Tue, Oct 26, 2021 at 11:37:30PM +0800, Ming Lei wrote:

quoted

OK, then Luis shouldn't consider livepatching as one such issue to solve
with one generic solution.

It's not what I was told when the deadlock was found with zram, so I was
informed quite the contrary.

From my perspective, it is quite easy to get it wrong due to either a lack 
of generic support, or missing rules/documentation.

Indeed. I agree some level of guidence is needed, even if subtle, rather
than tribal knowledge. I'll start off with the test_sysfs demo'ing what
not to do and documenting this there. I don't think it makes sense to
formalize yet documentation for "though shalt not do this" generically
until a full depth search is done with Coccinelle.

So if this thread 
leads to "do not share locks between a module removal and a sysfs 
operation" strict rule, it would be at least something.

I think that's where we are at. I'll wait to complete my coccinelle
deadlock hunt patch to complete the full search, and that could be
useful to *warn* aboute new use cases, so to prevent this deadlock
in the future. Until then I agree that the complexity introduced is
not worth it given the evidence of users, but the full evidence of
actual users still remains to be determined. A perfect job left to
advances with Coccinelle.

In the same 
manner as Luis proposed to document try_module_get() expectations.

Right and so sysfs ops using try_module_get() *still* remains safe,
and so will keep that patch in my next iteration because there *are*
*many* uses cases for that.

  Luis