| Date | Wed, 9 Dec 2009 19:15:52 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [patch 0/9] Fix various __task_cred related invalid RCU assumptions |
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On Wed, 9 Dec 2009, Paul E. McKenney wrote:
> On Thu, Dec 10, 2009 at 12:52:46AM -0000, Thomas Gleixner wrote: > > While auditing the read_lock(&tasklist_lock) sites for a possible > > conversion to rcu-read_lock() I stumbled over an unprotected user of > > __task_cred in kernel/sys.c > > > > That caused me to audit all the __task_cred usage sites except in > > kernel/exit.c. > > > > Most of the usage sites are correct, but some of them trip over > > invalid assumptions about the protection which is given by RCU. > > > > - spinlocked/preempt_disabled regions are equivalent to rcu_read_lock(): > > > > That's wrong. RCU does not guarantee that. > > > > It has been that way due to implementation details and it still is > > valid for CONFIG_TREE_PREEMPT_RCU=n, but there is no guarantee that > > this will be the case forever. > > To back this up, item #2 from Documentation/RCU/checklist.txt says:
Hmm. This seems to be a difference that the tree-RCU things introduced, no? I wonder if we have other areas where we just knew that a spinlock would make an rcu read-lock unnecessary (which used to be true..)
Linus
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