Message ID | 1421312314-72330-4-git-send-email-borntraeger@de.ibm.com (mailing list archive) |
---|---|
State | Not Applicable |
Delegated to: | Michael Ellerman |
Headers | show |
On 01/15/2015 09:58 AM, Christian Borntraeger wrote: > ACCESS_ONCE does not work reliably on non-scalar types. For > example gcc 4.6 and 4.7 might remove the volatile tag for such > accesses during the SRA (scalar replacement of aggregates) step > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) > > Change the p2m code to replace ACCESS_ONCE with READ_ONCE. > > Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Juergen Gross <jgross@suse.com> > --- > arch/x86/xen/p2m.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c > index edbc7a6..cb71016 100644 > --- a/arch/x86/xen/p2m.c > +++ b/arch/x86/xen/p2m.c > @@ -554,7 +554,7 @@ static bool alloc_p2m(unsigned long pfn) > mid_mfn = NULL; > } > > - p2m_pfn = pte_pfn(ACCESS_ONCE(*ptep)); > + p2m_pfn = pte_pfn(READ_ONCE(*ptep)); > if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) || > p2m_pfn == PFN_DOWN(__pa(p2m_missing))) { > /* p2m leaf page is missing */ >
On 15/01/15 08:58, Christian Borntraeger wrote: > ACCESS_ONCE does not work reliably on non-scalar types. For > example gcc 4.6 and 4.7 might remove the volatile tag for such > accesses during the SRA (scalar replacement of aggregates) step > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) > > Change the p2m code to replace ACCESS_ONCE with READ_ONCE. Acked-by: David Vrabel <david.vrabel@citrix.com> Let me know if you want me to merge this via the Xen tree. David
Am 15.01.2015 um 11:43 schrieb David Vrabel: > On 15/01/15 08:58, Christian Borntraeger wrote: >> ACCESS_ONCE does not work reliably on non-scalar types. For >> example gcc 4.6 and 4.7 might remove the volatile tag for such >> accesses during the SRA (scalar replacement of aggregates) step >> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) >> >> Change the p2m code to replace ACCESS_ONCE with READ_ONCE. > > Acked-by: David Vrabel <david.vrabel@citrix.com> Thanks > Let me know if you want me to merge this via the Xen tree. With your Acked-by, I can easily carry this in my tree. We can then ensure that this patch is merged before the ACCESS_ONCE is made stricter - making bisecting easier. Christian
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c index edbc7a6..cb71016 100644 --- a/arch/x86/xen/p2m.c +++ b/arch/x86/xen/p2m.c @@ -554,7 +554,7 @@ static bool alloc_p2m(unsigned long pfn) mid_mfn = NULL; } - p2m_pfn = pte_pfn(ACCESS_ONCE(*ptep)); + p2m_pfn = pte_pfn(READ_ONCE(*ptep)); if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) || p2m_pfn == PFN_DOWN(__pa(p2m_missing))) { /* p2m leaf page is missing */
ACCESS_ONCE does not work reliably on non-scalar types. For example gcc 4.6 and 4.7 might remove the volatile tag for such accesses during the SRA (scalar replacement of aggregates) step (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) Change the p2m code to replace ACCESS_ONCE with READ_ONCE. Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> --- arch/x86/xen/p2m.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)