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authorHugh Dickins <hugh@veritas.com>2007-08-31 04:26:50 +0100
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-08-30 21:54:31 -0700
commit62e6f1e8bb7c48c02b8bdb3085c5f6365682149b (patch)
tree975277fdd906c173bf48bfbe0226b80bb0e14529
parenta1c582d0720f2eff61043e90711767decf37b917 (diff)
downloadlinux-62e6f1e8bb7c48c02b8bdb3085c5f6365682149b.tar.gz
fix maxcpus=1 oops in show_stat()
Alexey Dobriyan reports that maxcpus=1 is still broken in 2.6.23-rc4: if CONFIG_HOTPLUG_CPU is not set, x86_64 bootup oopses in show_stat() - for_each_possible_cpu accesses a per-cpu area which was never set up. Alexey identified commit 61ec7567db103d537329b0db9a887db570431ff4 (ACPI: boot correctly with "nosmp" or "maxcpus=0") as the origin; but it's not really to blame, just exposes a bug in 2.6.23-rc1's commit 8b3b295502444340dd0701855ac422fbf32e161d (Especially when !CONFIG_HOTPLUG_CPU, avoid needlessy allocating resources for CPUs that can never become available). rc1's test for max_cpus < 2 in start_kernel() wasn't working because max_cpus was still NR_CPUS at that point: until rc4 moved the maxcpus parsing earlier. Now it sets cpu_possible_map to 1 before allocating all possible per-cpu areas; then smp_init() expands cpu_possible_map to cpu_present_map (0xf in my case) later on. rc1's commit has good intentions, but expects cpu_present_map to be limited by maxcpus, which is only the case on i386. cpus_and(possible, possible,present) might be good, but needs an audit of cpu_present_map uses - there may well be assumptions that any cpu present is possible. So stay safe for now and just revert those #ifndef CONFIG_HOTPLUG_CPU optimizations in rc1's commit. Signed-off-by: Hugh Dickins <hugh@veritas.com> Cc: Alexey Dobriyan <adobriyan@sw.ru> Cc: Len Brown <lenb@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jan Beulich <jbeulich@novell.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--init/main.c8
1 files changed, 0 insertions, 8 deletions
diff --git a/init/main.c b/init/main.c
index 450e6ee52ab..9def935ab13 100644
--- a/init/main.c
+++ b/init/main.c
@@ -397,10 +397,6 @@ static void __init smp_init(void)
{
unsigned int cpu;
-#ifndef CONFIG_HOTPLUG_CPU
- cpu_possible_map = cpu_present_map;
-#endif
-
/* FIXME: This should be done in userspace --RR */
for_each_present_cpu(cpu) {
if (num_online_cpus() >= max_cpus)
@@ -545,10 +541,6 @@ asmlinkage void __init start_kernel(void)
setup_arch(&command_line);
setup_command_line(command_line);
unwind_setup();
-#ifndef CONFIG_HOTPLUG_CPU
- if (max_cpus < 2)
- cpu_possible_map = cpu_online_map;
-#endif
setup_per_cpu_areas();
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */