Messages in this thread | | | Date | Tue, 4 Jul 2023 14:04:32 -0400 | From | "Liam R. Howlett" <> | Subject | Re: [mm] 408579cd62: WARNING:suspicious_RCU_usage |
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* Liam R. Howlett <Liam.Howlett@Oracle.com> [230704 11:25]: > * Oliver Sang <oliver.sang@intel.com> [230704 09:51]:
... > > > Ok, that is indeed a very different stack trace. > > > > > > So maybe the fix is a real fix, but the first complaint shut up > > > lockdep, so this is the *second* and unrelated complaint. > > > > > > And indeed: it turns out that do_vma_munmap() does this: > > > > > > ret = do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock); > > > validate_mm(mm); > > > > > > and so we have *another* validate_mm() that is now done outside the lock. > > > > > > That one is actually pretty pointless. We've *just* validated the mm > > > already inside do_vmi_align_munmap(), except we only did it in one of > > > the two return cases. > > > > > > So I think the fix is to just move that validate_mm() into the other > > > return case of do_vmi_align_munmap(), and remove it from the caller. > > > > > > IOW, something like the attached (NOTE! This is in *addition* to the > > > previous patch, which is the same as the one you quoted, just with > > > slightly different whitespace as commit ae80b4041984: "mm: validate > > > the mm before dropping the mmap lock"). > > > > Thanks a lot for guidance! > > I applied below patch directly upon ae80b4041984, and confirmed the > > WARNING gone. Thanks > > > > Thanks for testing this. > > I can clean more of this up now that the mmap locking has been changed. > For instance, we can drop a number of checks before a write (and all > read cases, if any remain) since there is no alteration without the > write lock.
Thanks Linus for fixing the two issues causing rcu warnings - my testing had lockdep & maple tree debug, so I'm still working on why my testing failed on the initial patch.
For the time being, I've used the config from the bot to test a larger cleanup of this code. I'll send it through the mm development as to get better test coverage.
Regards, Liam
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