From: Anshuman Khandual khandual@linux.vnet.ibm.com Subject: mm/mprotect: add a cond_resched() inside change_pmd_range()

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.

[ 850.962530] INFO: rcu_sched detected stalls on CPUs/tasks: [ 850.962584] 154-....: (670 ticks this GP) idle=022/140000000000000/0 softirq=2825/2825 fqs=612 [ 850.962605] (detected by 955, t=6002 jiffies, g=4486, c=4485, q=90864) [ 850.962895] Sending NMI from CPU 955 to CPUs 154: [ 850.992667] NMI backtrace for cpu 154 [ 850.993069] CPU: 154 PID: 147071 Comm: workload Not tainted 4.15.0-rc3+ #3 [ 850.993258] NIP: c0000000000b3f64 LR: c0000000000b33d4 CTR: 000000000000aa18 [ 850.993503] REGS: 00000000a4b0fb44 TRAP: 0501 Not tainted (4.15.0-rc3+) [ 850.993707] MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 22422082 XER: 00000000 [ 850.994386] CFAR: 00000000006cf8f0 SOFTE: 1 GPR00: 0010000000000000 c00003ef9b1cb8c0 c0000000010cc600 0000000000000000 GPR04: 8e0000018c32b200 40017b3858fd6e00 8e0000018c32b208 40017b3858fd6e00 GPR08: 8e0000018c32b210 40017b3858fd6e00 8e0000018c32b218 40017b3858fd6e00 GPR12: ffffffffffffffff c00000000fb25100 [ 850.995976] NIP [c0000000000b3f64] plpar_hcall9+0x44/0x7c [ 850.996174] LR [c0000000000b33d4] pSeries_lpar_flush_hash_range+0x384/0x420 [ 850.996401] Call Trace: [ 850.996600] [c00003ef9b1cb8c0] [c00003fa8fff7d40] 0xc00003fa8fff7d40 (unreliable) [ 850.996959] [c00003ef9b1cba40] [c0000000000688a8] flush_hash_range+0x48/0x100 [ 850.997261] [c00003ef9b1cba90] [c000000000071b14] __flush_tlb_pending+0x44/0xd0 [ 850.997600] [c00003ef9b1cbac0] [c000000000071fa8] hpte_need_flush+0x408/0x470 [ 850.997958] [c00003ef9b1cbb30] [c0000000002c646c] change_protection_range+0xaac/0xf10 [ 850.998180] [c00003ef9b1cbcb0] [c0000000002f2510] change_prot_numa+0x30/0xb0 [ 850.998502] [c00003ef9b1cbce0] [c00000000013a950] task_numa_work+0x2d0/0x3e0 [ 850.998816] [c00003ef9b1cbda0] [c00000000011ea30] task_work_run+0x130/0x190 [ 850.999121] [c00003ef9b1cbe00] [c00000000001bcd8] do_notify_resume+0x118/0x120 [ 850.999421] [c00003ef9b1cbe30] [c00000000000b744] ret_from_except_lite+0x70/0x74 [ 850.999716] Instruction dump: [ 850.999959] 60000000 f8810028 7ca42b78 7cc53378 7ce63b78 7d074378 7d284b78 7d495378 [ 851.000575] 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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/mprotect.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff -puN mm/mprotect.c~mm-mprotect-add-a-cond_resched-inside-change_pmd_range mm/mprotect.c --- a/mm/mprotect.c~mm-mprotect-add-a-cond_resched-inside-change_pmd_range +++ a/mm/mprotect.c @@ -166,7 +166,7 @@ static inline unsigned long change_pmd_r next = pmd_addr_end(addr, end); if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && !pmd_devmap(*pmd) && pmd_none_or_clear_bad(pmd)) - continue; + goto next;

/* invoke the mmu notifier if the pmd is populated */ if (!mni_start) { @@ -188,7 +188,7 @@ static inline unsigned long change_pmd_r }

/* huge pmd was handled */ - continue; + goto next; } } /* fall through, the trans huge pmd just split */ @@ -196,6 +196,8 @@ static inline unsigned long change_pmd_r this_pages = change_pte_range(vma, pmd, addr, next, newprot, dirty_accountable, prot_numa); pages += this_pages; +next: + cond_resched(); } while (pmd++, addr = next, addr != end);

if (mni_start) _