On Sun, 31 May 2015 10:51:17 -0700 Joe Perches <[email protected]> wrote:
> On Wed, 2015-05-27 at 14:19 -0700, Andrew Morton wrote: > > On Wed, 27 May 2015 14:09:31 -0700 Joe Perches <[email protected]> wrote: > > > > > > Problems when CONFIG_PREEMPT=n. > > > > > > > > > + down_read(&mm->mmap_sem); > > > > > + vma = find_vma(mm, ip); > > > > > + if (vma && vma->vm_file) { > > > > > + struct file *f = vma->vm_file; > > > > > + char *gfp_buf = (char *)__get_free_page(GFP_KERNEL); > > > > > > > > We shouldn't assume we can use GFP_KERNEL here. Even if the > > > > preempt_count() worked, we might be in a context which requires > > > > GFP_NOFS or GFP_NOIO. > > > > > > This code is basically a copy of the existing print_vma_addr() > > > so is that true for all the existing uses too? > > > > Yeah, the current code is pretty junky. But normally print_vma_addr() > > should never be called so nobody noticed... > > > > In e8bff74a Ingo did a fiddle to preempt_conditional_sti() which looks > > like it will address the CONFIG_PREEMPT=n issue, but only on x86. > > Maybe this? (using GFP_ATOMIC and __GFP_NOWARN) (tries to remember what this is about) Please do include the (updated) changelog each time. This is intended to replace open-coded calls to print_vma_addr(), yes? We shouldn't really need the memory allocation at all - we could poke these characters one at a time into the log buffer. That would require quite some hackery with d_path which would be rather pointless. Maybe for this purpose it's sufficient to just grab vma->vm_file->f_path->dentry->d_name. It's not as if this is terribly important code. But we still have the down_read(mmap_sem) in there. I don't immediately see any deadlocks in the current callsites but it isn't obvious. I dunno, I just don't think it's a nice idea to be allocating memory and taking mmap_sem and doing rcu_read_lock (in d_path) all within core vsprintf/printk. printk() is supposed to be callable from virtually any context, not "any context as long as you don't use features X Y and Z". If we can make print_vma_addr() robust then OK. Perhaps we just don't try to print the vma's filename. People can look up the hex address in /proc/pid/maps if it's really needed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
