>Our platform use sdhci host controller. And now there's a discussion to schedule
>inside sdhci_request() function of drivers/mmc/host/sdhci.c.
>According to the mmc stack code, seems the sdhci_request() is in the context
>of kernel thread (mmcqd), so I think it should be OK if schedule inside of it.
>
>But when I tried it with below patch:
>---------------------------------------------------------------------------
>diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>index 5dead05..2c2ac66 100644
>--- a/drivers/mmc/host/sdhci.c
>+++ b/drivers/mmc/host/sdhci.c
>@@ -1184,6 +1184,10 @@ static void sdhci_request(struct mmc_host *mmc, struct
>mmc_request *mrq)
>
> host = mmc_priv(mmc);
>
>+ printk(KERN_ERR "%s: Enter into sdhci_request:\n",
>mmc_hostname(host->mmc));
>+ msleep(10);
>+ printk(KERN_ERR "%s: Go on after msleep 10ms ...\n",
>mmc_hostname(host->mmc));
>+
> spin_lock_irqsave(&host->lock, flags);
>
> WARN_ON(host->mrq != NULL);
>---------------------------------------------------------------------------
>The kernel reported 'scheduling while atomic' BUG as below:
>---------------------------------------------------------------------------
>...
><3>[ 4.985928] mmc0: Enter into sdhci_request:
><3>[ 4.996750] mmc0: Go on after msleep 10ms ...
><3>[ 5.007822] mmc0: Enter into sdhci_request:
><3>[ 5.018790] mmc0: Go on after msleep 10ms ...
><3>[ 5.028727] mmc0: Enter into sdhci_request:
><3>[ 5.039841] mmc0: Go on after msleep 10ms ...
><3>[ 5.049772] mmc0: Enter into sdhci_request:
><3>[ 5.049815] BUG: scheduling while atomic: swapper/0/0x00000104
><4>[ 5.049845] no locks held by swapper/0.
><4>[ 5.049866] Modules linked in:
><4>[ 5.049889] Modules linked in:
><4>[ 5.049912]
><4>[ 5.049930] Pid: 0, comm: swapper Not tainted 2.6.35.3+ #8 /
><4>[ 5.049960] EIP: 0060:[<c152ab86>] EFLAGS: 00000206 CPU: 0
><4>[ 5.049997] EIP is at _raw_spin_unlock_irq+0x25/0x3b
><4>[ 5.050024] EAX: c1751f28 EBX: c2607bc0 ECX: 00000007 EDX: 00000007
><4>[ 5.050055] ESI: c1779a1c EDI: f74400b0 EBP: c1751f2c ESP: c1751f28
><4>[ 5.050086] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
><0>[ 5.050116] Process swapper (pid: 0, ti=c1750000 task=c176dea0
>task.ti=c1750000)
><0>[ 5.050150] Stack:
><4>[ 5.050165] c2607bc0 c1751f58 c10288bc 00000000 00000002 00000000
>c1028865 c176dea0
><4>[ 5.050229] <0> 00000001 c184cbc0 f74400b0 c176dea0 c1751fb4 c15285f8
>2c66255a 00000001
><4>[ 5.050300] <0> c184cbc0 c1845000 c184cbc0 c184cbc0 c184cbc0 f74400b0
>00000000 c176e108
><0>[ 5.050376] Call Trace:
><4>[ 5.050407] [<c10288bc>] ? finish_task_switch+0x57/0x90
><4>[ 5.050441] [<c1028865>] ? finish_task_switch+0x0/0x90
><4>[ 5.050474] [<c15285f8>] ? schedule+0x78e/0x869
><4>[ 5.050509] [<c10584ef>] ? tick_nohz_restart_sched_tick+0x154/0x15d
><4>[ 5.050545] [<c100192c>] ? cpu_idle+0x6a/0x76
><4>[ 5.050576] [<c150a524>] ? rest_init+0xd4/0xd9
><4>[ 5.050609] [<c17f28bb>] ? start_kernel+0x2f7/0x2fc
><4>[ 5.050642] [<c17f20d0>] ? i386_start_kernel+0xd0/0xd7
><0>[ 5.050667] Code: fc b0 ff 5b 5d c3 55 ba 01 00 00 00 89 e5 8b 4d 04 53
>89 c3 8d 40 10 e8 97 2b b3 ff 89 d8 e8 f0 b2 cb ff e8 84 06 b3 ff fb 89 e0 <25>
>00 e0 ff ff ff 48 14 f6 40 08 08 74 05 e8 e0 dc ff ff 5b 5d
><4>[ 5.051060] Call Trace:
><4>[ 5.051088] [<c10288bc>] finish_task_switch+0x57/0x90
><4>[ 5.051121] [<c1028865>] ? finish_task_switch+0x0/0x90
><4>[ 5.051153] [<c15285f8>] schedule+0x78e/0x869
><4>[ 5.051185] [<c10584ef>] ? tick_nohz_restart_sched_tick+0x154/0x15d
><4>[ 5.051221] [<c100192c>] cpu_idle+0x6a/0x76
><4>[ 5.051250] [<c150a524>] rest_init+0xd4/0xd9
><4>[ 5.051280] [<c17f28bb>] start_kernel+0x2f7/0x2fc
><4>[ 5.051312] [<c17f20d0>] i386_start_kernel+0xd0/0xd7
><3>[ 5.051340] bad: scheduling from the idle thread!
><4>[ 5.051368] Pid: 0, comm: swapper Not tainted 2.6.35.3+ #8
><4>[ 5.051393] Call Trace:
><4>[ 5.051415] [<c1527b01>] ? printk+0xf/0x11
><4>[ 5.051444] [<c10251ff>] dequeue_task_idle+0x1a/0x27
><4>[ 5.051475] [<c1029a0a>] dequeue_task+0xca/0xd9
><4>[ 5.051506] [<c1029a38>] deactivate_task+0x1f/0x25
><4>[ 5.051535] [<c1527fb9>] schedule+0x14f/0x869
><4>[ 5.051567] [<c105b212>] ? trace_hardirqs_on+0xb/0xd
><4>[ 5.051598] [<c1528b59>] schedule_timeout+0x27c/0x2cf
><4>[ 5.051630] [<c104101a>] ? process_timeout+0x0/0xa
><4>[ 5.051662] [<c1528bc1>] schedule_timeout_uninterruptible+0x15/0x17
><4>[ 5.051723] [<c10414cd>] msleep+0x10/0x16
><4>[ 5.051758] [<c1372c45>] sdhci_request+0x33/0xfc
><4>[ 5.051790] [<c136a3a5>] mmc_request_done+0x42/0x6a
><4>[ 5.051820] [<c1373603>] sdhci_tasklet_finish+0xc4/0xca
><4>[ 5.051854] [<c1039e7c>] tasklet_action+0x69/0xb0
><4>[ 5.051883] [<c103a4bc>] __do_softirq+0x122/0x27a
><4>[ 5.051912] [<c103a63f>] do_softirq+0x2b/0x43
><4>[ 5.051940] [<c103a7cf>] irq_exit+0x35/0x72
><4>[ 5.051969] [<c101643f>] smp_apic_timer_interrupt+0x6e/0x7c
><4>[ 5.052002] [<c152b4ab>] apic_timer_interrupt+0x2f/0x34
><4>[ 5.052035] [<c105007b>] ? down_trylock+0x18/0x27
><4>[ 5.052064] [<c152ab86>] ? _raw_spin_unlock_irq+0x25/0x3b
><4>[ 5.052097] [<c10288bc>] finish_task_switch+0x57/0x90
><4>[ 5.052129] [<c1028865>] ? finish_task_switch+0x0/0x90
><4>[ 5.052159] [<c15285f8>] schedule+0x78e/0x869
><4>[ 5.052190] [<c10584ef>] ? tick_nohz_restart_sched_tick+0x154/0x15d
><4>[ 5.052224] [<c100192c>] cpu_idle+0x6a/0x76
><4>[ 5.052252] [<c150a524>] rest_init+0xd4/0xd9
><4>[ 5.052282] [<c17f28bb>] start_kernel+0x2f7/0x2fc
><4>[ 5.052312] [<c17f20d0>] i386_start_kernel+0xd0/0xd7
><1>[ 5.062718] BUG: unable to handle kernel NULL pointer dereference at
>(null)
><1>[ 5.062774] IP: [<(null)>] (null)
><4>[ 5.062806] *pdpt = 0000000001856001 *pde = 0000000000000000
><0>[ 5.062851] Oops: 0010 [#1] PREEMPT SMP
><0>[ 5.062890] last sysfs file:
><4>[ 5.062917] Modules linked in:
><4>[ 5.062944]
><4>[ 5.062967] Pid: 0, comm: swapper Not tainted 2.6.35.3+ #8 /
><4>[ 5.063003] EIP: 0060:[<00000000>] EFLAGS: 00010046 CPU: 1
><4>[ 5.063037] EIP is at 0x0
><4>[ 5.063061] EAX: c2607bc0 EBX: c15304d4 ECX: 00000001 EDX: c176dea0
><4>[ 5.063099] ESI: c176dea0 EDI: c2607bc0 EBP: f747de3c ESP: f747de28
><4>[ 5.063137] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
><0>[ 5.063173] Process swapper (pid: 0, ti=f747c000 task=f747a230
>task.ti=f747c000)
><0>[ 5.063216] Stack:
><4>[ 5.063236] c10298a7 00000001 c2607bc0 c176dea0 c2607bc0 f747de48
>c10298d3 00000000
><4>[ 5.063309] <0> f747de70 c1031fad 00000000 00000001 00000001 00000000
>00000282 c1751dd8
><4>[ 5.063394] <0> c1751e18 f747debc f747de78 c1032183 f747de80 c1041022
>f747ded0 c1040b47
><0>[ 5.063488] Call Trace:
><4>[ 5.063520] [<c10298a7>] ? enqueue_task+0x72/0x7f
><4>[ 5.063559] [<c10298d3>] ? activate_task+0x1f/0x25
><4>[ 5.063597] [<c1031fad>] ? try_to_wake_up+0x268/0x416
><4>[ 5.063636] [<c1032183>] ? wake_up_process+0xf/0x11
><4>[ 5.063674] [<c1041022>] ? process_timeout+0x8/0xa
><4>[ 5.063712] [<c1040b47>] ? run_timer_softirq+0x299/0x414
><4>[ 5.063752] [<c104101a>] ? process_timeout+0x0/0xa
><4>[ 5.063790] [<c103a4bc>] ? __do_softirq+0x122/0x27a
><4>[ 5.063828] [<c103a63f>] ? do_softirq+0x2b/0x43
><4>[ 5.063864] [<c103a7cf>] ? irq_exit+0x35/0x72
><4>[ 5.063900] [<c101643f>] ? smp_apic_timer_interrupt+0x6e/0x7c
><4>[ 5.063942] [<c152b4ab>] ? apic_timer_interrupt+0x2f/0x34
><4>[ 5.063984] [<c105007b>] ? down_trylock+0x18/0x27
><4>[ 5.064022] [<c1209a63>] ? intel_idle+0x169/0x1aa
><4>[ 5.064062] [<c13676bd>] ? cpuidle_idle_call+0x71/0x14c
><4>[ 5.064101] [<c100190b>] ? cpu_idle+0x49/0x76
><4>[ 5.064138] [<c152514f>] ? start_secondary+0x1c1/0x1c6
><0>[ 5.064171] Code: Bad EIP value.
><0>[ 5.064208] EIP: [<00000000>] 0x0 SS:ESP 0068:f747de28
><0>[ 5.064251] CR2: 0000000000000000
><6>[ 0.000000] Initializing cgroup subsys cpu
><5>[ 0.000000] Linux version 2.6.35.3+ (root@yunpeng) (gcc version 4.4.4
>20100630 (Red Hat 4.4.4-10) (GCC) ) #8 SMP PREEMPT Wed Jan 26 22:49:08 CST 2011
>---------------------------------------------------------------------------
According to the call trace, in the mmc_request_done() of drivers/mmc/core/core.c, it will retry to issue the same command as below:
------------------------------------------------
if (err && cmd->retries) {
...
host->ops->request(host, mrq);
-----------------------------------------------
Since the mmc_request_done() is called in the tasklet context, so it's not surprise why kernel reports BUG once mmc_request_done() try to re-send command to card.
Thanks.
Regards,
Yunpeng
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