Re: [RFC] [PATCH 2.6.37-rc5-tip 8/20] 8: uprobes: mmap and forkhooks.

From: Peter Zijlstra
Date: Wed Jan 26 2011 - 05:20:16 EST

On Wed, 2011-01-26 at 14:33 +0530, Srikar Dronamraju wrote:
> I actually dont like to release the write_lock and then reacquire it.
> write_opcode, which is called thro install_uprobe, i.e to insert the
> actual breakpoint instruction takes a read lock on the mmap_sem.
> Hence uprobe_mmap gets called in context with write lock on mmap_sem
> held, I had to release it before calling install_uprobe.

Ah, right, so that's going to give you a head-ache ;-)

The moment you release this mmap_sem, the map you're going to install
the probe point in can go away.

The only way to make this work seems to start by holding the mmap_sem
for writing and make a breakpoint install function that assumes its
taken and doesn't try to acquire it again.

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