linux-kernel - [tip:x86/urgent] x86/numa_emulation: Fix uniform-split numa emulation

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Date:   Tue, 30 Oct 2018 03:39:51 -0700
From:   tip-bot for Dave Jiang <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com, dan.j.williams@...el.com,
        peterz@...radead.org, tglx@...utronix.de, luto@...nel.org,
        bp@...en8.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        hpa@...or.com, dave.jiang@...el.com,
        alexander.h.duyck@...ux.intel.com
Subject: [tip:x86/urgent] x86/numa_emulation: Fix uniform-split numa
 emulation

Commit-ID:  c6ee7a548e2c291398b4f32c1f741c66b9f98e1c
Gitweb:     https://git.kernel.org/tip/c6ee7a548e2c291398b4f32c1f741c66b9f98e1c
Author:     Dave Jiang <dave.jiang@...el.com>
AuthorDate: Thu, 25 Oct 2018 13:26:45 -0700
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 30 Oct 2018 11:36:43 +0100

x86/numa_emulation: Fix uniform-split numa emulation

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

Fixes: 1f6a2c6d9f121 ("x86/numa_emulation: Introduce uniform split capability")
Signed-off-by: Dave Jiang <dave.jiang@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/154049911459.2685845.9210186007479774286.stgit@dwillia2-desk3.amr.corp.intel.com

---
 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) {