On Wed, 2009-08-26 at 21:15 +0530, Amit Shah wrote: > [cc'ing some people who have made some commits in hvc_console.c] > > On (Wed) Aug 26 2009 [16:57:18], Amit Shah wrote: > > On (Tue) Aug 25 2009 [11:47:20], Amit Shah wrote: > > > > > > Hello all, > > > > > > Here is a new iteration of the patch series that implements a > > > transport for guest and host communications. > > > > > > The code has been updated to reuse the virtio-console device instead > > > of creating a new virtio-serial device. > > > > And the problem now is that hvc calls the put_chars function with > > spinlocks held and we now allocate pages in send_buf(), called from > > put_chars. > > > > A few solutions: > > [snip] > > > - Convert hvc's usage of spinlocks to mutexes. I've no idea how this > > will play out; I'm no expert here. But I did try doing this and so far > > it all looks OK. No lockups, lockdep warnings, nothing. I have full > > debugging enabled. But this doesn't mean it's right. > > So just to test this further I added the capability to have more than > one hvc console spawn from virtio_console, created two consoles and did > a 'cat' of a file in each of the virtio-consoles. It's been running for > half an hour now without any badness. No spew in debug logs too. > > I also checked the code in hvc_console.c that takes the spin_locks. > Nothing there that runs from (or needs to run from) interrupt context. > So the change to mutexes does seem reasonable. Also, the spinlock code > was added really long back -- git blame shows Linus' first git commit > introduced them in the git history, so it's pure legacy baggage. I won't tell Ryan you called his code "pure legacy baggage" if you don't ;) http://git.kernel.org/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commitdiff;h=d450b4ae023fb4be175389c18f4f87677da03020 cheers
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