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| author | Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com> | 2017-08-03 08:20:22 +0200 |
|---|---|---|
| committer | Ralf Baechle <ralf@linux-mips.org> | 2017-08-07 11:57:30 +0200 |
| commit | 6f542ebeaee0ee552a902ce3892220fc22c7ec8e (patch) | |
| tree | bc45179de8f2b095c21e5988e78e9ede06d82200 | |
| parent | 00e06297b351d286199c6cf542ea70b8fbabafee (diff) | |
| download | linux-6f542ebeaee0ee552a902ce3892220fc22c7ec8e.tar.gz | |
MIPS: Fix race on setting and getting cpu_online_mask
While testing cpu hoptlug (cpu down and up in loops) on kernel 4.4, it was
observed that occasionally check for cpu online will fail in kernel/cpu.c,
_cpu_up:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/kernel/cpu.c?h=v4.4.79#n485
518 /* Arch-specific enabling code. */
519 ret = __cpu_up(cpu, idle);
520
521 if (ret != 0)
522 goto out_notify;
523 BUG_ON(!cpu_online(cpu));
Reason is race between start_secondary and _cpu_up. cpu_callin_map is set
before cpu_online_mask. In __cpu_up, cpu_callin_map is waited for, but cpu
online mask is not, resulting in race in which secondary processor started
and set cpu_callin_map, but not yet set the online mask,resulting in above
BUG being hit.
Upstream differs in the area. cpu_online check is in bringup_wait_for_ap,
which is after cpu reached AP_ONLINE_IDLE,where secondary passed its start
function. Nonetheless, fix makes start_secondary safe and not depending on
other locks throughout the code. It protects as well against cpu_online
checks put in between sometimes in the future.
Fix this by moving completion after all flags are set.
Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>
Cc: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16925/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
| -rw-r--r-- | arch/mips/kernel/smp.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c index 770d4d1516cbb1..6bace7695788fb 100644 --- a/arch/mips/kernel/smp.c +++ b/arch/mips/kernel/smp.c @@ -376,9 +376,6 @@ asmlinkage void start_secondary(void) cpumask_set_cpu(cpu, &cpu_coherent_mask); notify_cpu_starting(cpu); - complete(&cpu_running); - synchronise_count_slave(cpu); - set_cpu_online(cpu, true); set_cpu_sibling_map(cpu); @@ -386,6 +383,9 @@ asmlinkage void start_secondary(void) calculate_cpu_foreign_map(); + complete(&cpu_running); + synchronise_count_slave(cpu); + /* * irq will be enabled in ->smp_finish(), enabling it too early * is dangerous. |