Messages in this thread | | | Date | Mon, 14 Feb 2011 10:51:13 -0500 | From | Jason Baron <> | Subject | Re: [PATCH 0/2] jump label: 2.6.38 updates |
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On Sat, Feb 12, 2011 at 07:47:45PM +0100, Peter Zijlstra wrote: > On Fri, 2011-02-11 at 22:38 +0100, Peter Zijlstra wrote: > > > > So why can't we make that jump_label_entry::refcount and > > jump_label_key::state an atomic_t and be done with it? > > So I had a bit of a poke at this because I didn't quite understand why > all that stuff was as it was. I applied both Jason's patches and then > basically rewrote kernel/jump_label.c just for kicks ;-) > > I haven't tried compiling this, let alone running it, but provided I > didn't actually forget anything the storage per key is now 16 bytes when > modules are disabled and 24 * (1 + mods) bytes for when they are > enabled. The old code had 64 + 40 * mods bytes. > > I still need to clean up the static_branch_else bits and look at !x86 > aside from the already mentioned bits.. but what do people think? > > ---
Generally, I really like this! Its the direction I think the jump label code should be going. The complete removal of the hash table, makes the design a lot better and simpler. We just need to get some of the details cleaned up, and of course we need this to compile :) But I don't see any fundamental problems with this approach.
Things that still need to be sorted out:
1) Since jump_label.h, are included in kernel.h, (indirectly via the dynamic_debug.h) the atomic_t definitions could be problematic, since atomic.h includes kernel.h indirectly...so we might need some header magic.
2) I had some code to disallow writing to module __init section, by setting the 'key' value to 0, after the module->init was run, but before, the memory was freed. And then I check for a non-zero key value when the jump label is updated. In this way we can't corrupt some random piece of memory. I had this done via the 'MODULE_STATE_LIVE' notifier.
3) For 'jump_label_enable()' 'jump_label_disable()' in the tracepoint code, I'm not sure that there is an enable for each disable. So i'm not sure if a refcount would work there. But we can fix this by first checking 'jump_label_enabled()' before calling 'jump_label_eanble()' or jump_label_ref(). This is safe b/c the the tracepoint code is protected using the tracepoint_mutex.
thanks,
-Jason
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