[PATCH 3.13.y-ckt 091/103] libata: prevent HSM state change race between ISR and PIO

Kamal Mostafa
2015-02-19T00:38:51Z

From: David Jeffery <djeffery@redhat.com>

commit ce7514526742c0898b837d4395f515b79dfb5a12 upstream.

It is possible for ata_sff_flush_pio_task() to set ap->hsm_task_state to
HSM_ST_IDLE in between the time __ata_sff_port_intr() checks for HSM_ST_IDLE
and before it calls ata_sff_hsm_move() causing ata_sff_hsm_move() to BUG().

This problem is hard to reproduce making this patch hard to verify, but this
fix will prevent the race.

I have not been able to reproduce the problem, but here is a crash dump from
a 2.6.32 kernel.

On examining the ata port's state, its hsm_task_state field has a value of HSM_ST_IDLE:

crash> struct ata_port.hsm_task_state ffff881c1121c000
hsm_task_state = 0

Normally, this should not be possible as ata_sff_hsm_move() was called from ata_sff_host_intr(),
which checks hsm_task_state and won't call ata_sff_hsm_move() if it has a HSM_ST_IDLE value.

PID: 11053 TASK: ffff8816e846cae0 CPU: 0 COMMAND: "sshd"
#0 [ffff88008ba03960] machine_kexec at ffffffff81038f3b
#1 [ffff88008ba039c0] crash_kexec at ffffffff810c5d92
#2 [ffff88008ba03a90] oops_end at ffffffff8152b510
#3 [ffff88008ba03ac0] die at ffffffff81010e0b
#4 [ffff88008ba03af0] do_trap at ffffffff8152ad74
#5 [ffff88008ba03b50] do_invalid_op at ffffffff8100cf95
#6 [ffff88008ba03bf0] invalid_op at ffffffff8100bf9b
[exception RIP: ata_sff_hsm_move+317]
RIP: ffffffff813a77ad RSP: ffff88008ba03ca0 RFLAGS: 00010097
RAX: 0000000000000000 RBX: ffff881c1121dc60 RCX: 0000000000000000
RDX: ffff881c1121dd10 RSI: ffff881c1121dc60 RDI: ffff881c1121c000
RBP: ffff88008ba03d00 R8: 0000000000000000 R9: 000000000000002e
R10: 000000000001003f R11: 000000000000009b R12: ffff881c1121c000
R13: 0000000000000000 R14: 0000000000000050 R15: ffff881c1121dd78
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#7 [ffff88008ba03d08] ata_sff_host_intr at ffffffff813a7fbd
#8 [ffff88008ba03d38] ata_sff_interrupt at ffffffff813a821e
#9 [ffff88008ba03d78] handle_IRQ_event at ffffffff810e6ec0
--- <IRQ stack> ---
[exception RIP: pipe_poll+48]
RIP: ffffffff81192780 RSP: ffff880f26d459b8 RFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff880f26d459c8 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff881a0539fa80
RBP: ffffffff8100bb8e R8: ffff8803b23324a0 R9: 0000000000000000
R10: ffff880f26d45dd0 R11: 0000000000000008 R12: ffffffff8109b646
R13: ffff880f26d45948 R14: 0000000000000246 R15: 0000000000000246
ORIG_RAX: ffffffffffffff10 CS: 0010 SS: 0018
RIP: 00007f26017435c3 RSP: 00007fffe020c420 RFLAGS: 00000206
RAX: 0000000000000017 RBX: ffffffff8100b072 RCX: 00007fffe020c45c
RDX: 00007f2604a3f120 RSI: 00007f2604a3f140 RDI: 000000000000000d
RBP: 0000000000000000 R8: 00007fffe020e570 R9: 0101010101010101
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fffe020e5f0
R13: 00007fffe020e5f4 R14: 00007f26045f373c R15: 00007fffe020e5e0
ORIG_RAX: 0000000000000017 CS: 0033 SS: 002b

Somewhere between the ata_sff_hsm_move() check and the ata_sff_host_intr() check, the value changed.
On examining the other cpus to see what else was running, another cpu was running the error handler
routines:

PID: 326 TASK: ffff881c11014aa0 CPU: 1 COMMAND: "scsi_eh_1"
#0 [ffff88008ba27e90] crash_nmi_callback at ffffffff8102fee6
#1 [ffff88008ba27ea0] notifier_call_chain at ffffffff8152d515
#2 [ffff88008ba27ee0] atomic_notifier_call_chain at ffffffff8152d57a
#3 [ffff88008ba27ef0] notify_die at ffffffff810a154e
#4 [ffff88008ba27f20] do_nmi at ffffffff8152b1db
#5 [ffff88008ba27f50] nmi at ffffffff8152aaa0
[exception RIP: _spin_lock_irqsave+47]
RIP: ffffffff8152a1ff RSP: ffff881c11a73aa0 RFLAGS: 00000006
RAX: 0000000000000001 RBX: ffff881c1121deb8 RCX: 0000000000000000
RDX: 0000000000000246 RSI: 0000000000000020 RDI: ffff881c122612d8
RBP: ffff881c11a73aa0 R8: ffff881c17083800 R9: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff881c1121c000
R13: 000000000000001f R14: ffff881c1121dd50 R15: ffff881c1121dc60
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0000
--- <NMI exception stack> ---
#6 [ffff881c11a73aa0] _spin_lock_irqsave at ffffffff8152a1ff
#7 [ffff881c11a73aa8] ata_exec_internal_sg at ffffffff81396fb5
#8 [ffff881c11a73b58] ata_exec_internal at ffffffff81397109
#9 [ffff881c11a73bd8] atapi_eh_request_sense at ffffffff813a34eb

Before it tried to acquire a spinlock, ata_exec_internal_sg() called ata_sff_flush_pio_task().
This function will set ap->hsm_task_state to HSM_ST_IDLE, and has no locking around setting this
value. ata_sff_flush_pio_task() can then race with the interrupt handler and potentially set
HSM_ST_IDLE at a fatal moment, which will trigger a kernel BUG.

v2: Fixup comment in ata_sff_flush_pio_task()

tj: Further updated comment. Use ap->lock instead of shost lock and
use the [un]lock_irq variant instead of the irqsave/restore one.

Signed-off-by: David Milburn <dmilburn@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/ata/libata-sff.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index 37acda6..136803c 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -1333,7 +1333,19 @@ void ata_sff_flush_pio_task(struct ata_port *ap)
DPRINTK("ENTER\n");

cancel_delayed_work_sync(&ap->sff_pio_task);
+
+ /*
+ * We wanna reset the HSM state to IDLE. If we do so without
+ * grabbing the port lock, critical sections protected by it which
+ * expect the HSM state to stay stable may get surprised. For
+ * example, we may set IDLE in between the time
+ * __ata_sff_port_intr() checks for HSM_ST_IDLE and before it calls
+ * ata_sff_hsm_move() causing ata_sff_hsm_move() to BUG().
+ */
+ spin_lock_irq(ap->lock);
ap->hsm_task_state = HSM_ST_IDLE;
+ spin_unlock_irq(ap->lock);
+
ap->sff_pio_task_link = NULL;

if (ata_msg_ctl(ap))
--
1.9.1