Messages in this thread | | | Subject | Re: [PATCH v4 5/5] md: protect md_thread with rcu | From | Yu Kuai <> | Date | Tue, 4 Apr 2023 09:34:46 +0800 |
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Hi, Logan!
在 2023/04/03 23:53, Logan Gunthorpe 写道: >> >> /* caller need to make sured returned md_thread won't be freed */ >> -static inline struct md_thread *get_md_thread(struct md_thread *t) >> +static inline struct md_thread *get_md_thread(struct md_thread __rcu *t) >> { >> - return t; >> + return rcu_access_pointer(t); > > This should not be using rcu_access_pointer(). That function is only > appropriate when the value of t is not being dereferenced. This should > be using rcu_dereference_protected() with some reasoning as to why it's > safe to use this function. It might make sense to open code this for > every call site if the reasoning is different in each location. > Preferrably the second argument in the check should be some lockdep > condition that ensures this. If that's not possible, a comment > explaining the reasoning why it is safe in all the call sites should be > added here.
Yes, it's right rcu_dereference_protected() should be used here, I need to take a look at each call site from patch 3 and figure out if they're safe without rcu protection.
> > On one hand this is looking like my idea of using RCU is producing more > churn than the spin lock. On the other hand I think it's cleaning up and > documenting more unsafe use cases (like other potentially unsafe > accesses of the the thread pointer). So I still think the RCU is a good > approach here.
Yes, some other unsafe accesses is protected now in this patch. I'll send a new version soon.
Thanks, Kuai
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