On Wed, Oct 27, 2021 at 01:57:40PM +0200, Miroslav Benes wrote:
On Tue, 26 Oct 2021, Luis Chamberlain wrote:
On Tue, Oct 26, 2021 at 11:37:30PM +0800, Ming Lei wrote:
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