Messages in this thread | | | Date | Tue, 24 Jan 2023 20:36:53 +0100 | Subject | Re: [PATCH] tools/memory-model Flag suspicious use of srcu cookies | From | Jonas Oberhauser <> |
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On 1/24/2023 8:15 PM, Paul E. McKenney wrote: > On Tue, Jan 24, 2023 at 12:19:24PM -0500, Alan Stern wrote: >> On Tue, Jan 24, 2023 at 03:39:51PM +0100, Jonas Oberhauser wrote: >>> The herd model of LKMM deviates from actual implementations in the >>> range of cookies that might be returned by srcu_lock() and similar >>> functions. As a consequence, code that relies on srcu_lock() >>> returning specific values might pass on the herd model but fail in >>> the real world. >>> >>> This patch flags any code that looks at the value of a cookie >>> without passing it on to an srcu_unlock(). This indicates that the >>> cookie value might be being used in ways that can lead herd to >>> produce incorrect results, as in the following (contrived) case: >>> >>> P0(struct srcu_struct *ss) >>> { >>> int r = srcu_read_lock(ss); >>> if (r==0) >>> srcu_read_unlock(ss, r); >>> } >>> >>> Without this patch, the code passes herd7 without any warnings. >>> >>> With this patch, this code is flagged with illegal-srcu-cookie-ctrl, >>> indicating that a cookie is used to compute a control condition. >>> Such scenarios potentially lead to other branches of the code that >>> are possible in real usage not being evaluated by herd7. In this >>> example, this affects the branch where r!=0, which would lead to >>> an unmatched read side critical section and thus to hangs of >>> synchronize_srcu() calls. >>> >>> Besides use of cookies in control conditions, the patch also flags >>> use in address computation and any time a cookie is inspected but >>> not later passed to srcu_read_unlock(). >>> >>> Signed-off-by: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com> >>> --- >> Acked-by: Alan Stern <stern@rowland.harvard.edu> > Thank you both! > > I wordsmithed the commit log as follows, but then realized that this > depends on Alan's earlier patch.
Yeah, I don't know if I did this correctly. I based it on the lkmm-srcu.2023.01.20a branch. Let me know if I should have done this differently.
Looking through your changes to learn for future submissions:
> [...] > > This patch flags any code that looks at the value of a cookie > without passing it on to an srcu_unlock().
You missed this one : )
Have fun, jonas
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