[PATCH] percpu: fix chunk range calculation
Tim Hartrick
tim at edgecast.com
Mon Nov 21 11:20:15 EST 2011
Dave,
I will give it a try ASAP. Unfortunately, ASAP won't be until Friday.
tim
On Nov 20, 2011 6:43 PM, "Dave Young" <dyoung at redhat.com> wrote:
> On 11/19/2011 02:55 AM, Tejun Heo wrote:
>
> > Percpu allocator recorded the cpus which map to the first and last
> > units in pcpu_first/last_unit_cpu respectively and used them to
> > determine the address range of a chunk - e.g. it assumed that the
> > first unit has the lowest address in a chunk while the last unit has
> > the highest address.
> >
> > This simply isn't true. Groups in a chunk can have arbitrary positive
> > or negative offsets from the previous one and there is no guarantee
> > that the first unit occupies the lowest offset while the last one the
> > highest.
> >
> > Fix it by actually comparing unit offsets to determine cpus occupying
> > the lowest and highest offsets. Also, rename pcu_first/last_unit_cpu
> > to pcpu_low/high_unit_cpu to avoid confusion.
> >
> > The chunk address range is used to flush cache on vmalloc area
> > map/unmap and decide whether a given address is in the first chunk by
> > per_cpu_ptr_to_phys() and the bug was discovered by invalid
> > per_cpu_ptr_to_phys() translation for crash_note.
> >
> > Kudos to Dave Young for tracking down the problem.
>
>
> Tejun, thanks
>
> Now that if addr is not in first trunk it must be in vmalloc area, below
> logic should be right:
> if (in_first_chunk) {
> if (!is_vmalloc_addr(addr))
> return __pa(addr);
> else
> return page_to_phys(vmalloc_to_page(addr));
> } else
> if (!is_vmalloc_addr(addr)) /* not possible */
> return __pa(addr);
> else
> return page_to_phys(pcpu_addr_to_page(addr));
>
> So how about just simply remove in first chunk checking to simplify the
> code as followging:
>
> phys_addr_t per_cpu_ptr_to_phys(void *addr)
> {
> if (!is_vmalloc_addr(addr))
> return __pa(addr);
> else
> return page_to_phys(pcpu_addr_to_page(addr));
> }
>
> >
> > Signed-off-by: Tejun Heo <tj at kernel.org>
> > Reported-by: WANG Cong <xiyou.wangcong at gmail.com>
> > Reported-by: Dave Young <dyoung at redhat.com>
> > LKML-Reference: <4EC21F67.10905 at redhat.com>
> > Cc: stable @kernel.org
> > ---
> > Heh, that's a stupid bug. Can you please verify this fixes the
> > problem?
>
>
> I can confirm that the per cpu translation works with this patch, but I
> have not managed to finished kdump test because kexec tools refuse
> to load the crash kernel. I need more debugging on kexec tools.
>
> Tim, could you help to test if this patch works for your kdump case?
>
> >
> > Thank you very much.
> >
> > mm/percpu-vm.c | 12 ++++++------
> > mm/percpu.c | 34 ++++++++++++++++++++--------------
> > 2 files changed, 26 insertions(+), 20 deletions(-)
> >
> > diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> > index ea53496..bfad724 100644
> > --- a/mm/percpu-vm.c
> > +++ b/mm/percpu-vm.c
> > @@ -143,8 +143,8 @@ static void pcpu_pre_unmap_flush(struct pcpu_chunk
> *chunk,
> > int page_start, int page_end)
> > {
> > flush_cache_vunmap(
> > - pcpu_chunk_addr(chunk, pcpu_first_unit_cpu, page_start),
> > - pcpu_chunk_addr(chunk, pcpu_last_unit_cpu, page_end));
> > + pcpu_chunk_addr(chunk, pcpu_low_unit_cpu, page_start),
> > + pcpu_chunk_addr(chunk, pcpu_high_unit_cpu, page_end));
> > }
> >
> > static void __pcpu_unmap_pages(unsigned long addr, int nr_pages)
> > @@ -206,8 +206,8 @@ static void pcpu_post_unmap_tlb_flush(struct
> pcpu_chunk *chunk,
> > int page_start, int page_end)
> > {
> > flush_tlb_kernel_range(
> > - pcpu_chunk_addr(chunk, pcpu_first_unit_cpu, page_start),
> > - pcpu_chunk_addr(chunk, pcpu_last_unit_cpu, page_end));
> > + pcpu_chunk_addr(chunk, pcpu_low_unit_cpu, page_start),
> > + pcpu_chunk_addr(chunk, pcpu_high_unit_cpu, page_end));
> > }
> >
> > static int __pcpu_map_pages(unsigned long addr, struct page **pages,
> > @@ -284,8 +284,8 @@ static void pcpu_post_map_flush(struct pcpu_chunk
> *chunk,
> > int page_start, int page_end)
> > {
> > flush_cache_vmap(
> > - pcpu_chunk_addr(chunk, pcpu_first_unit_cpu, page_start),
> > - pcpu_chunk_addr(chunk, pcpu_last_unit_cpu, page_end));
> > + pcpu_chunk_addr(chunk, pcpu_low_unit_cpu, page_start),
> > + pcpu_chunk_addr(chunk, pcpu_high_unit_cpu, page_end));
> > }
> >
> > /**
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index bf80e55..93b5a7c 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -116,9 +116,9 @@ static int pcpu_atom_size __read_mostly;
> > static int pcpu_nr_slots __read_mostly;
> > static size_t pcpu_chunk_struct_size __read_mostly;
> >
> > -/* cpus with the lowest and highest unit numbers */
> > -static unsigned int pcpu_first_unit_cpu __read_mostly;
> > -static unsigned int pcpu_last_unit_cpu __read_mostly;
> > +/* cpus with the lowest and highest unit addresses */
> > +static unsigned int pcpu_low_unit_cpu __read_mostly;
> > +static unsigned int pcpu_high_unit_cpu __read_mostly;
> >
> > /* the address of the first chunk which starts with the kernel static
> area */
> > void *pcpu_base_addr __read_mostly;
> > @@ -984,19 +984,19 @@ phys_addr_t per_cpu_ptr_to_phys(void *addr)
> > {
> > void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
> > bool in_first_chunk = false;
> > - unsigned long first_start, first_end;
> > + unsigned long first_low, first_high;
> > unsigned int cpu;
> >
> > /*
> > - * The following test on first_start/end isn't strictly
> > + * The following test on unit_low/high isn't strictly
> > * necessary but will speed up lookups of addresses which
> > * aren't in the first chunk.
> > */
> > - first_start = pcpu_chunk_addr(pcpu_first_chunk,
> pcpu_first_unit_cpu, 0);
> > - first_end = pcpu_chunk_addr(pcpu_first_chunk, pcpu_last_unit_cpu,
> > - pcpu_unit_pages);
> > - if ((unsigned long)addr >= first_start &&
> > - (unsigned long)addr < first_end) {
> > + first_low = pcpu_chunk_addr(pcpu_first_chunk, pcpu_low_unit_cpu,
> 0);
> > + first_high = pcpu_chunk_addr(pcpu_first_chunk, pcpu_high_unit_cpu,
> > + pcpu_unit_pages);
> > + if ((unsigned long)addr >= first_low &&
> > + (unsigned long)addr < first_high) {
> > for_each_possible_cpu(cpu) {
> > void *start = per_cpu_ptr(base, cpu);
> >
> > @@ -1233,7 +1233,9 @@ int __init pcpu_setup_first_chunk(const struct
> pcpu_alloc_info *ai,
> >
> > for (cpu = 0; cpu < nr_cpu_ids; cpu++)
> > unit_map[cpu] = UINT_MAX;
> > - pcpu_first_unit_cpu = NR_CPUS;
> > +
> > + pcpu_low_unit_cpu = NR_CPUS;
> > + pcpu_high_unit_cpu = NR_CPUS;
> >
> > for (group = 0, unit = 0; group < ai->nr_groups; group++, unit +=
> i) {
> > const struct pcpu_group_info *gi = &ai->groups[group];
> > @@ -1253,9 +1255,13 @@ int __init pcpu_setup_first_chunk(const struct
> pcpu_alloc_info *ai,
> > unit_map[cpu] = unit + i;
> > unit_off[cpu] = gi->base_offset + i *
> ai->unit_size;
> >
> > - if (pcpu_first_unit_cpu == NR_CPUS)
> > - pcpu_first_unit_cpu = cpu;
> > - pcpu_last_unit_cpu = cpu;
> > + /* determine low/high unit_cpu */
> > + if (pcpu_low_unit_cpu == NR_CPUS ||
> > + unit_off[cpu] < unit_off[pcpu_low_unit_cpu])
> > + pcpu_low_unit_cpu = cpu;
> > + if (pcpu_high_unit_cpu == NR_CPUS ||
> > + unit_off[cpu] > unit_off[pcpu_high_unit_cpu])
> > + pcpu_high_unit_cpu = cpu;
> > }
> > }
> > pcpu_nr_units = unit;
> >
> > _______________________________________________
> > kexec mailing list
> > kexec at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
>
>
>
> --
> Thanks
> Dave
>
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