linux-kernel - [PATCH v3] x86/numa_emulation: Fix uniform-split numa emulation

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Message-ID: <154049911459.2685845.9210186007479774286.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Thu, 25 Oct 2018 13:26:45 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     mingo@...hat.com
Cc:     x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        stable@...r.kernel.org, Dave Jiang <dave.jiang@...el.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] x86/numa_emulation: Fix uniform-split numa emulation

From: Dave Jiang <dave.jiang@...el.com>

The numa_emulation() routine in the 'uniform' case walks through all the
physical 'memblk' instances and divides them into N emulated nodes with
split_nodes_size_interleave_uniform(). As each physical node is consumed
it is removed from the physical memblk array in the
numa_remove_memblk_from() helper. Since
split_nodes_size_interleave_uniform() handles advancing the array as the
'memblk' is consumed it is expected that the base of the array is always
specified as the argument.

Otherwise, on multi-socket (> 2) configurations the uniform-split
capability can generate an invalid numa configuration leading to boot
failures with signatures like the following:

    rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
    Sending NMI from CPU 0 to CPUs 2:
    NMI backtrace for cpu 2
    CPU: 2 PID: 1332 Comm: pgdatinit0 Not tainted 4.19.0-rc8-next-20181019-baseline #59
    RIP: 0010:__init_single_page.isra.74+0x81/0x90
    [..]
    Call Trace:
     deferred_init_pages+0xaa/0xe3
     deferred_init_memmap+0x18f/0x318
     kthread+0xf8/0x130
     ? deferred_free_pages.isra.105+0xc9/0xc9
     ? kthread_stop+0x110/0x110
     ret_from_fork+0x35/0x40

Cc: x86@...nel.org
Cc: Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: <stable@...r.kernel.org>
Fixes: 1f6a2c6d9f121 ("x86/numa_emulation: Introduce uniform split capability")
Signed-off-by: Dave Jiang <dave.jiang@...el.com>
Tested-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
Changes since v2: https://lore.kernel.org/patchwork/patch/988541/

* Update the changelog with details from testing by Alex

 arch/x86/mm/numa_emulation.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/numa_emulation.c b/arch/x86/mm/numa_emulation.c
index b54d52a2d00a..d71d72cf6c66 100644
--- a/arch/x86/mm/numa_emulation.c
+++ b/arch/x86/mm/numa_emulation.c
@@ -400,9 +400,17 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 		n = simple_strtoul(emu_cmdline, &emu_cmdline, 0);
 		ret = -1;
 		for_each_node_mask(i, physnode_mask) {
+			/*
+			 * The reason we pass in blk[0] is due to
+			 * numa_remove_memblk_from() called by
+			 * emu_setup_memblk() will delete entry 0
+			 * and then move everything else up in the pi.blk
+			 * array. Therefore we should always be looking
+			 * at blk[0].
+			 */
 			ret = split_nodes_size_interleave_uniform(&ei, &pi,
-					pi.blk[i].start, pi.blk[i].end, 0,
-					n, &pi.blk[i], nid);
+					pi.blk[0].start, pi.blk[0].end, 0,
+					n, &pi.blk[0], nid);
 			if (ret < 0)
 				break;
 			if (ret < n) {