Messages in this thread | | | Subject | Re: [PATCH] arm64: Neaten show_regs, remove KERN_CONT | From | Joe Perches <> | Date | Tue, 25 Oct 2016 09:44:23 -0700 |
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(adding Linus Torvalds)
On Tue, 2016-10-25 at 15:32 +0100, Mark Rutland wrote: > On Mon, Oct 24, 2016 at 09:27:57AM -0700, Joe Perches wrote: > > On Mon, 2016-10-24 at 12:31 +0100, Mark Rutland wrote: > > > On Sun, Oct 23, 2016 at 01:40:49PM -0700, Joe Perches wrote: > > > > commit db4b0710fae9 ("arm64: fix show_regs fallout from KERN_CONT changes") > > > > corrected the KERN_CONT fallout from commit 4bcc595ccd80 > > > > ("printk: reinstate KERN_CONT for printing continuation lines"), but > > > > the code still has unnecessary KERN_CONT uses. Remove them. > > > > > > Why are these unnecessary KERN_CONTs a larger problem than duplicating > > > the format string for a third time? Having to duplicate it at all was > > > annoying enough. > > > > Not printing partial lines is the best solution to avoiding > > message output interleaving. > > Looking further, it seems that KERN_CONT is terminally broken. The core > code somehow swallows newlines from some KERN_CONT prints in a > non-deterministic fashion, and also appears to insert newlines from thin > air. This happens in the absence of intervening printks. > > With the current code in v4.9-rc2, we get output like: > > x29: 0000ffffe4938c80 x28: 0000000000000000 > x27: 0000000000000000 x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 > x23: 0000000000000000 x22: 0000000000000000 > x21: 0000000000400470 x20: 0000000000000000 > x19: 0000000000000000 x18: 0000ffffe4938b60 > x17: 0000000000411000 x16: 0000ffff82f72c9c > x15: 0000ffff830c8000 x14: 0000000000000040 > x13: 0000ffff830c8028 x12: 0000000000008738 > x11: 0000000000000008 > x10: 00000000ffffffff > x9 : 0000ffff830b4e40 x8 : 2f2f2f2f2f2f2f2f > x7 : b3b3bab7acff8b8a x6 : 0000ffff83097aa8 > x5 : 54d58839205d3679 x4 : 0000000000000000 > x3 : 00000000004005d0 x2 : ffff000000000000 > x1 : 0000ffffe4938e08 x0 : ffff000000000000 > > ... or: > > x29: 0000fffff6f6a600 x28: 0000000000000000 x27: 0000000000000000 x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 x23: 0000000000000000 x22: 0000000000000000 x21: 0000000000400470 x20: 0000000000000000 x19: 0000000000000000 x18: 0000fffff6f6a4e0 x17: 0000000000411000 x16: 0000ffffa6e1fc9c x15: 0000ffffa6f75000 x14: 0000000000000040 > x13: 0000ffffa6f75028 x12: 0000000000008738 x11: 0000000000000008 x10: 00000000ffffffff > x9 : 0000ffffa6f61e40 x8 : 2f2f2f2f2f2f2f2f x7 : b3b3bab7acff8b8a x6 : 0000ffffa6f44aa8 > x5 : 874b6ebb9d5e2f3d x4 : 0000000000000000 x3 : 00000000004005d0 x2 : ffff000000000000 > x1 : 0000fffff6f6a788 x0 : ffff000000000000 > > ... and of course, the buffer shown by $(dmesg) or $(demsg -T) is equally > insane, but different. > > I found that adding a space prior to newlines prevented them from being > swallowed, but $(dmesg) would still suffer from random additions. > > Given all that, unless the core code is changed to as to behave > deterministically at least for trivial cases like this one, I think we > should avoid KERN_CONT like the plague. > > So FWIW, so long as you fold in the changes I requested in my other > reply, please add: > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > ... I'll go fix up show_pte() without pr_cont(). > > Thanks, > Mark.
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