Messages in this thread | | | Date | Wed, 17 Jul 2013 16:16:02 -0700 | From | David Daney <> | Subject | Re: [PATCH RFC] lib: Make radix_tree_node_alloc() irq safe |
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On 07/17/2013 04:12 PM, Andrew Morton wrote: > On Tue, 16 Jul 2013 19:06:30 +0200 Jan Kara <jack@suse.cz> wrote: > >> With users of radix_tree_preload() run from interrupt (CFQ is one such >> possible user), the following race can happen: >> >> radix_tree_preload() >> ... >> radix_tree_insert() >> radix_tree_node_alloc() >> if (rtp->nr) { >> ret = rtp->nodes[rtp->nr - 1]; >> <interrupt> >> ... >> radix_tree_preload() >> ... >> radix_tree_insert() >> radix_tree_node_alloc() >> if (rtp->nr) { >> ret = rtp->nodes[rtp->nr - 1]; >> >> And we give out one radix tree node twice. That clearly results in radix >> tree corruption with different results (usually OOPS) depending on which >> two users of radix tree race. >> >> Fix the problem by disabling interrupts when working with rtp variable. >> In-interrupt user can still deplete our preloaded nodes but at least we >> won't corrupt radix trees. >> >> ... >> >> There are some questions regarding this patch: >> Do we really want to allow in-interrupt users of radix_tree_preload()? CFQ >> could certainly do this in older kernels but that particular call site where I >> saw the bug hit isn't there anymore so I'm not sure this can really happen with >> recent kernels. > > Well, it was never anticipated that interrupt-time code would run > radix_tree_preload(). The whole point in the preloading was to be able > to perform GFP_KERNEL allocations before entering the spinlocked region > which needs to allocate memory. > > Doing all that from within an interrupt is daft, because the interrupt code > can't use GFP_KERNEL anyway. > >> Also it is actually harmful to do preloading if you are in interrupt context >> anyway. The disadvantage of disallowing radix_tree_preload() in interrupt is >> that we would need to tweak radix_tree_node_alloc() to somehow recognize >> whether the caller wants it to use preloaded nodes or not and that callers >> would have to get it right (although maybe some magic in radix_tree_preload() >> could handle that). >> >> Opinions? > > BUG_ON(in_interrupt()) :)
Is is really that severe? How about...
WARN_ON() instead?
David Daney
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