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Commit c5cae661d6cf808b6984762f763261adf35f3eb7

Authored by Ian Campbell
1 parent 7284ce6c9f
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

xen: fix hang on suspend. 

In 65f63384 "xen: improve error handling in do_suspend" I said:
    - xs_suspend()/xs_resume() and dpm_suspend_noirq()/dpm_resume_noirq() were not
      nested in the obvious way.
and changed the ordering of the calls as so:
    BEFORE		AFTER
    xs_suspend		dpm_suspend_noirq
    dpm_suspend_noirq	xs_suspend
    *SUSPEND*		*SUSPEND*
    dpm_resume_noirq	dpm_resume_noirq
    xs_resume		xs_resume
Clearly this is not an improvement and I was talking rubbish.

In particular the new ordering is susceptible to a hang if a xenstore write is
in progress at the point at which the suspend kicks in. When the suspend
process calls xs_suspend it tries to take the request_mutex but if a write is
in progress it could be looping in xenbus_xs.c:read_reply() waiting for
something to arrive on &xs_state.reply_list while holding the request_mutex
(taken in the caller of read_reply).

However if we have done dpm_suspend_noirq before xs_suspend then we won't get
any more xenstore interrupts and process_msg() will never be woken up to add
anything to the reply_list.

Fix this by calling xs_suspend before dpm_suspend_noirq. If dpm_suspend_noirq
fails then make sure we go through the xs_suspend_cancel() code path.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stable Kernel <stable@kernel.org>

Showing 1 changed file with 4 additions and 4 deletions Side-by-side Diff

drivers/xen/manage.c
Diff comments   View file @ c5cae66
... ... @@ -102,15 +102,15 @@
102 102 goto out_thaw;
103 103 }
104 104  
  105 + printk(KERN_DEBUG "suspending xenstore...\n");
  106 + xs_suspend();
  107 +
105 108 err = dpm_suspend_noirq(PMSG_SUSPEND);
106 109 if (err) {
107 110 printk(KERN_ERR "dpm_suspend_noirq failed: %d\n", err);
108 111 goto out_resume;
109 112 }
110 113  
111   - printk(KERN_DEBUG "suspending xenstore...\n");
112   - xs_suspend();
113   -
114 114 err = stop_machine(xen_suspend, &cancelled, cpumask_of(0));
115 115  
116 116 dpm_resume_noirq(PMSG_RESUME);
117 117  
... ... @@ -120,13 +120,13 @@
120 120 cancelled = 1;
121 121 }
122 122  
  123 +out_resume:
123 124 if (!cancelled) {
124 125 xen_arch_resume();
125 126 xs_resume();
126 127 } else
127 128 xs_suspend_cancel();
128 129  
129   -out_resume:
130 130 dpm_resume_end(PMSG_RESUME);
131 131  
132 132 /* Make sure timer events get retriggered on all CPUs */