On Wed, Aug 22, 2007 at 11:04:22AM -0700, Andrew Morton wrote: > On Wed, 22 Aug 2007 12:00:11 -0500 > Dean Nelson <[EMAIL PROTECTED]> wrote: > > > > > 3) WARNING: declaring multiple variables together should be avoided > > > > checkpatch.pl is erroneously commplaining about the following found in five > > different functions in arch/ia64/sn/kernel/xpmem_pfn.c. > > > > int n_pgs = xpmem_num_of_pages(vaddr, size); > > What warning does it generate here?
The WARNING #3 above "declaring multiple variables together should be avoided". There is only one variable being declared, which happens to be initialized by the function xpmem_num_of_pages(). > > > - xpmem_fault_handler() appears to have imposed a kernel-wide rule that > > > when taking multiple mmap_sems, one should take the lowest-addressed one > > > first? If so, that probably wants a mention in that locking comment in > > > filemap.c > > > > Sure. After looking at the lock ordering comment block in mm/filemap.c, it > > wasn't clear to me how best to document this. Any suggestions/help would > > be most appreciated. > > umm, > > * when taking multiple mmap_sems, one should take the lowest-addressed one > * first > > ;) Thanks. > > > - xpmem_fault_handler() does atomic_dec(&seg_tg->mm->mm_users). What > > > happens if that was the last reference? > > > > When /dev/xpmem is opened by a user process, xpmem_open() incs mm_users > > and when it is flushed, xpmem_flush() decs it (via mmput()) after having > > ensured that no XPMEM attachments exist of this mm. Thus the dec in > > xpmem_fault_handler() will never take it to 0. > > OK. Generally if a reviewer asks a question like this, it indicates that a > code comment is needed. Because it is likely that others will later wonder > the same thing. Will do. > > > - Has it all been tested with lockdep enabled? Jugding from all the use > > > of SPIN_LOCK_UNLOCKED, it has not. > > > > > > Oh, ia64 doesn't implement lockdep. For this code, that is deeply > > > regrettable. > > > > No, it hasn't been tested with lockdep. But I have switched it from using > > SPIN_LOCK_UNLOCKED to spin_lock_init(). > > > > > ! This code all predates the nopage->fault conversion and won't work in > > > current kernels. > > > > I've switched from using nopage to using fault. I read that it is intended > > that nopfn also goes away. If this is the case, then the BUG_ON if VM_PFNMAP > > is set would make __do_fault() a rather unfriendly replacement for > > do_no_pfn(). > > > > > - xpmem_attach() does smp_processor_id() in preemptible code. Lucky that > > > ia64 doesn't do preempt? > > > > Actually, the code is fine as is even with preemption configured on. All > > it's > > doing is ensuring that the thread was previously pinned to the CPU it's > > currently running on. If it is, it can't be moved to another CPU via > > preemption, and if it isn't, the check will fail and we'll return -EINVAL > > and all is well. > > OK. Running smp_processor_id() from within preemptible code will generate > a warning, but the code is sneaky enough to prevent that warning if the > calling task happens to be pinned to a single CPU. Would it make more sense in this particular case to replace the call to smp_processor_id() in xpmem_attach() with a call to raw_smp_processor_id() instead, and add a comment explaining why? - 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/
