[PATCH 3.2 082/140] mm/mprotect: add a cond_resched() inside change_pmd_range()

Ben Hutchings
2018-02-28T17:25:08Z

From: Anshuman Khandual <khandual@linux.vnet.ibm.com>

commit 4991c09c7c812dba13ea9be79a68b4565bb1fa4e upstream.

While testing on a large CPU system, detected the following RCU stall
many times over the span of the workload. This problem is solved by
adding a cond_resched() in the change_pmd_range() function.

INFO: rcu_sched detected stalls on CPUs/tasks:
154-....: (670 ticks this GP) idle=022/140000000000000/0 softirq=2825/2825 fqs=612
(detected by 955, t=6002 jiffies, g=4486, c=4485, q=90864)
Sending NMI from CPU 955 to CPUs 154:
NMI backtrace for cpu 154
CPU: 154 PID: 147071 Comm: workload Not tainted 4.15.0-rc3+ #3
NIP: c0000000000b3f64 LR: c0000000000b33d4 CTR: 000000000000aa18
REGS: 00000000a4b0fb44 TRAP: 0501 Not tainted (4.15.0-rc3+)
MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 22422082 XER: 00000000
CFAR: 00000000006cf8f0 SOFTE: 1
GPR00: 0010000000000000 c00003ef9b1cb8c0 c0000000010cc600 0000000000000000
GPR04: 8e0000018c32b200 40017b3858fd6e00 8e0000018c32b208 40017b3858fd6e00
GPR08: 8e0000018c32b210 40017b3858fd6e00 8e0000018c32b218 40017b3858fd6e00
GPR12: ffffffffffffffff c00000000fb25100
NIP [c0000000000b3f64] plpar_hcall9+0x44/0x7c
LR [c0000000000b33d4] pSeries_lpar_flush_hash_range+0x384/0x420
Call Trace:
flush_hash_range+0x48/0x100
__flush_tlb_pending+0x44/0xd0
hpte_need_flush+0x408/0x470
change_protection_range+0xaac/0xf10
change_prot_numa+0x30/0xb0
task_numa_work+0x2d0/0x3e0
task_work_run+0x130/0x190
do_notify_resume+0x118/0x120
ret_from_except_lite+0x70/0x74
Instruction dump:
60000000 f8810028 7ca42b78 7cc53378 7ce63b78 7d074378 7d284b78 7d495378
e9410060 e9610068 e9810070 44000022 <7d806378> e9810028 f88c0000 f8ac0008

Link: http://lkml.kernel.org/r/20171214140551.5794-1-khandual@linux.vnet.ibm.com
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Suggested-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
mm/mprotect.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -92,13 +92,15 @@ static inline void change_pmd_range(stru
if (next - addr != HPAGE_PMD_SIZE)
split_huge_page_pmd(vma->vm_mm, pmd);
else if (change_huge_pmd(vma, pmd, addr, newprot))
- continue;
+ goto next;
/* fall through */
}
if (pmd_none_or_clear_bad(pmd))
- continue;
+ goto next;
change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
dirty_accountable);
+next:
+ cond_resched();
} while (pmd++, addr = next, addr != end);
}