Re: [linux-next][bisected c64e09ce] sysctl command hung indefinitely

On Sat 19-08-17 15:49:31, Abdul Haleem wrote:

quoted

Hi Michal,

'sysctl -a' command never completes on my PowerPC machine with latest
next kernel (As of next-20170811)

Machine Type : Power8 bare-metal
Kernel version : 4.13.0-rc4-next-20170817
gcc version : 4.8.5


command output
--------------
$ sysctl -a
[...
vm.hugetlb_shm_group = 0
vm.laptop_mode = 0
vm.legacy_va_layout = 0
vm.lowmem_reserve_ratio = 256	256	32
vm.max_map_count = 65530
vm.min_free_kbytes = 6637
vm.min_slab_ratio = 5
vm.min_unmapped_ratio = 1
vm.mmap_min_addr = 4096
vm.mmap_rnd_bits = 14
vm.mmap_rnd_compat_bits = 7
vm.nr_hugepages = 0
vm.nr_hugepages_mempolicy = 0
vm.nr_overcommit_hugepages = 0
vm.nr_pdflush_threads = 0
vm.numa_zonelist_order = Node
vm.numa_zonelist_order = e
vm.numa_zonelist_order = ode
vm.numa_zonelist_order = 
vm.numa_zonelist_order = de
vm.numa_zonelist_order = Node
vm.numa_zonelist_order = e
vm.numa_zonelist_order = ode
vm.numa_zonelist_order = 
vm.numa_zonelist_order = de
vm.numa_zonelist_order = Node
vm.numa_zonelist_order = e
vm.numa_zonelist_order = ode
vm.numa_zonelist_order = 
vm.numa_zonelist_order = de
vm.numa_zonelist_order = Node
vm.numa_zonelist_order = e
vm.numa_zonelist_order = ode
....]

The last string 'vm.numa_zonelist_order = ' keeps flooding the stdout
and command never exit.

A bisection resulted commit c64e09ce mm, page_alloc: rip out
ZONELIST_ORDER_ZONE

Yeah, my read implementation is broken. I do not update the ppos and so
the reader doesn't know it should exit. Mel was suggesting to keep the
proc_dostring but I thought I was more clever. Sigh...

This should do the trick. Andrew, could you fold it into
mm-page_alloc-rip-out-zonelist_order_zone.patch please?

Thanks for the report Abdul!

---
commit 69885605ee3ba681deb54021e3df645f46589ba1
Author: Michal Hocko [off-list ref]
Date:   Mon Aug 21 09:46:04 2017 +0200

    mmotm: mm-page_alloc-rip-out-zonelist_order_zone-fix
    
    Abdul has noticed that reading sysctl vm.numa_zonelist_order
    read will never terminate. This is because of
    http://lkml.kernel.org/r/20170714080006.7250-2-mhocko@kernel.org
    where the reading side doesn't update ppos and so the reader will
    never get 0. Return back to proc_dostring which does all the necessary
    stuff.
    
    Reported-by: Abdul Haleem [off-list ref]
    Signed-off-by: Michal Hocko [off-list ref]

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fda9afbd14d9..e7e92c8f4883 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h