On Fri, 26 Aug 2022, Will Deacon wrote: > On Thu, Aug 25, 2022 at 05:03:40PM -0400, Mikulas Patocka wrote: > > Here I reworked your patch, so that test_bit_acquire is defined just like > > test_bit. There's some code duplication (in > > include/asm-generic/bitops/generic-non-atomic.h and in > > arch/x86/include/asm/bitops.h), but that duplication exists in the > > test_bit function too. > > > > I tested it on x86-64 and arm64. On x86-64 it generates the "bt" > > instruction for variable-bit test and "shr; and $1" for constant bit test. > > On arm64 it generates the "ldar" instruction for both constant and > > variable bit test. > > > > For me, the kernel 6.0-rc2 doesn't boot in an arm64 virtual machine at all > > (with or without this patch), so I only compile-tested it on arm64. I have > > to bisect it. > > It's working fine for me and I haven't had any other reports that it's not > booting. Please could you share some more details about your setup so we > can try to reproduce the problem? I'm bisecting it now. I'll post the offending commit when I'm done. It gets stuck without printing anything at this point: Loading Linux 6.0.0-rc2 ... Loading initial ramdisk ... EFI stub: Booting Linux Kernel... EFI stub: Using DTB from configuration table EFI stub: Exiting boot services... I uploaded my .config here: https://people.redhat.com/~mpatocka/testcases/arm64-config/config-6.0.0-rc2 so you can try it on your own. The host system is MacchiatoBIN board with Debian 10.12. > This looks good to me, thanks for doing it! Just one thing that jumped out > at me: > > > Index: linux-2.6/include/linux/buffer_head.h > > =================================================================== > > --- linux-2.6.orig/include/linux/buffer_head.h > > +++ linux-2.6/include/linux/buffer_head.h > > @@ -156,7 +156,7 @@ static __always_inline int buffer_uptoda > > * make it consistent with folio_test_uptodate > > * pairs with smp_mb__before_atomic in set_buffer_uptodate > > */ > > - return (smp_load_acquire(&bh->b_state) & (1UL << BH_Uptodate)) != 0; > > + return test_bit_acquire(BH_Uptodate, &bh->b_state); > > Do you think it would be worth adding set_bit_release() and then relaxing > set_buffer_uptodate() to use that rather than the smp_mb__before_atomic()? > > Will Yes, we could add this (but it would be better to add it in a separate patch, so that backporting of the origianal patch to -stable is easier). Mikulas
