Messages in this thread | | | Date | Fri, 20 Apr 2012 13:22:06 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH] dma-debug: Fix deadlock with netconsole or other drivers that use the DMA API |
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On Thu, Apr 19, 2012 at 11:48:11AM -0700, Andrew Morton wrote: > On Thu, 19 Apr 2012 11:12:53 -0700 > Roland Dreier <roland@kernel.org> wrote: > > --- > > lib/dma-debug.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/lib/dma-debug.c b/lib/dma-debug.c > > index 13ef233..f198b4e 100644 > > --- a/lib/dma-debug.c > > +++ b/lib/dma-debug.c > > @@ -436,8 +436,8 @@ static struct dma_debug_entry *dma_entry_alloc(void) > > spin_lock_irqsave(&free_entries_lock, flags); > > > > if (list_empty(&free_entries)) { > > - pr_err("DMA-API: debugging out of memory - disabling\n"); > > global_disable = true; > > + pr_err("DMA-API: debugging out of memory - disabling\n"); > > goto out; > > } > > So *any* printk can deadlock if free_entries_lock is held and > global_disable==false? > > In that case we're going to need much sterner fixes. Any list_head > operation can do a printk if list_head debugging is enabled. > dma_debug_resize_entries() does a kfree() under free_entries_lock(!). > > Methinks we need a more general fix?
Hmm, I think the best way to fix it is to switch the hash-bucket lists to rcu. Then the lock is only needed in hash_bucket_add/del and we should be fine. But that is probably only a fix for the next merge window.
Joerg
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