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Subject[PATCH 3.4 113/176] libata: prevent HSM state change race between ISR and PIO
Date
From: David Jeffery <djeffery@redhat.com>

3.4.107-rc1 review patch. If anyone has any objections, please let me know.

------------------


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
---
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 3723e5e..fad2734 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


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