[PATCH v2] x86, mm: only wait for flushes from online cpus

[Mandeep Singh Baines <msb@xxxxxxxxxxxx>]

A cpu in the mm_cpumask could go offline before we send the invalidate
IPI causing us to wait forever. Avoid this by only waiting for online
cpus.

We are seeing a softlockup reporting during shutdown. The stack
trace shows us that we are inside default_send_IPI_mask_logical:

 BUG: soft lockup - CPU#0 stuck for 11s! [lmt-udev:23605]
 Pid: 23605, comm: lmt-udev Tainted: G        WC   3.2.7 #1
 EIP: 0060:[<8101eec6>] EFLAGS: 00000202 CPU: 0
 EIP is at flush_tlb_others_ipi+0x8a/0xba
 Call Trace:
  [<8101f0bb>] flush_tlb_mm+0x5e/0x62
  [<8101e36c>] pud_populate+0x2c/0x31
  [<8101e409>] pgd_alloc+0x98/0xc7
  [<8102c881>] mm_init.isra.38+0xcc/0xf3
  [<8102cbc2>] dup_mm+0x68/0x34e
  [<8139bbae>] ? _cond_resched+0xd/0x21
  [<810a5b7c>] ? kmem_cache_alloc+0x26/0xe2
  [<8102d421>] ? copy_process+0x556/0xda6
  [<8102d641>] copy_process+0x776/0xda6
  [<8102dd5e>] do_fork+0xcb/0x1d4
  [<810a8c96>] ? do_sync_write+0xd3/0xd3
  [<810a94ab>] ? vfs_read+0x95/0xa2
  [<81008850>] sys_clone+0x20/0x25
  [<8139d8c5>] ptregs_clone+0x15/0x30
  [<8139d7f7>] ? sysenter_do_call+0x12/0x26

Before the softlock, we see the following kernel warning:

 WARNING: at ../../arch/x86/kernel/apic/ipi.c:113 default_send_IPI_mask_logical+0x58/0x73()
 Pid: 23605, comm: lmt-udev Tainted: G         C   3.2.7 #1
 Call Trace:
  [<8102e666>] warn_slowpath_common+0x68/0x7d
  [<81016c36>] ? default_send_IPI_mask_logical+0x58/0x73
  [<8102e68f>] warn_slowpath_null+0x14/0x18
  [<81016c36>] default_send_IPI_mask_logical+0x58/0x73
  [<8101eec2>] flush_tlb_others_ipi+0x86/0xba
  [<8101f0bb>] flush_tlb_mm+0x5e/0x62
  [<8101e36c>] pud_populate+0x2c/0x31
  [<8101e409>] pgd_alloc+0x98/0xc7
  [<8102c881>] mm_init.isra.38+0xcc/0xf3
  [<8102cbc2>] dup_mm+0x68/0x34e
  [<8139bbae>] ? _cond_resched+0xd/0x21
  [<810a5b7c>] ? kmem_cache_alloc+0x26/0xe2
  [<8102d421>] ? copy_process+0x556/0xda6
  [<8102d641>] copy_process+0x776/0xda6
  [<8102dd5e>] do_fork+0xcb/0x1d4
  [<810a8c96>] ? do_sync_write+0xd3/0xd3
  [<810a94ab>] ? vfs_read+0x95/0xa2
  [<81008850>] sys_clone+0x20/0x25
  [<8139d8c5>] ptregs_clone+0x15/0x30
  [<8139d7f7>] ? sysenter_do_call+0x12/0x26

So we are sending an IPI to a cpu which is now offline. Once a cpu is offline,
it will no longer respond to IPIs. This explains the softlockup.

Addresses http://crosbug.com/31737

Changes in V2:
  * bitmap_and is not atomic so use a temporary bitmask

Signed-off-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxx>
Cc: Olof Johansson <olofj@xxxxxxxxxxxx>
---
 arch/x86/mm/tlb.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index d6c0418..231a0b9 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -185,6 +185,8 @@ static void flush_tlb_others_ipi(const struct cpumask *cpumask,
 	f->flush_mm = mm;
 	f->flush_va = va;
 	if (cpumask_andnot(to_cpumask(f->flush_cpumask), cpumask, cpumask_of(smp_processor_id()))) {
+		DECLARE_BITMAP(tmp_cpumask, NR_CPUS);
+
 		/*
 		 * We have to send the IPI only to
 		 * CPUs affected.
@@ -192,8 +194,13 @@ static void flush_tlb_others_ipi(const struct cpumask *cpumask,
 		apic->send_IPI_mask(to_cpumask(f->flush_cpumask),
 			      INVALIDATE_TLB_VECTOR_START + sender);
 
-		while (!cpumask_empty(to_cpumask(f->flush_cpumask)))
+		/* Only wait for online cpus */
+		do {
+			cpumask_and(to_cpumask(tmp_cpumask),
+				    to_cpumask(f->flush_cpumask),
+				    cpu_online_mask);
 			cpu_relax();
+		} while (!cpumask_empty(to_cpumask(tmp_cpumask)));
 	}
 
 	f->flush_mm = NULL;
-- 
1.7.7.3

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