Re: [Linux-stm32] [PATCH v9 22/33] counter: Internalize sysfs interface code

[William Breathitt Gray]

On Fri, Mar 12, 2021 at 04:02:42PM +0100, Fabrice Gasnier wrote:
> On 3/9/21 2:19 PM, William Breathitt Gray wrote:
> > +static ssize_t enums_available_show(const u32 *const enums,
> > +				    const size_t num_enums,
> > +				    const char *const strs[], char *buf)
> > +{
> > +	size_t len = 0;
> > +	size_t index;
> > +
> > +	for (index = 0; index < num_enums; index++)
> > +		len += sysfs_emit(buf + len, "%s\n", strs[enums[index]]);
> > +
> > +	return len;
> > +}
> > +
> > +static ssize_t strs_available_show(const struct counter_available *const avail,
> > +				   char *buf)
> > +{
> > +	size_t len = 0;
> > +	size_t index;
> > +
> > +	for (index = 0; index < avail->num_items; index++)
> > +		len += sysfs_emit(buf + len, "%s\n", avail->strs[index]);
> > +
> > +	return len;
> > +}
> 
> Hi William,
> 
> I was willing to do some testing on this series, on the stm32 counter
> drivers, since we released few fixes around them.
> 
> I tried to apply this series against current testing branch, with few
> patches applied (so it applies cleanly):
> - dt-bindings: counter: add interrupt-counter binding
> - counter: add IRQ or GPIO based counter
> - counter: stm32-timer-cnt: fix ceiling miss-alignment with reload register
> - counter: stm32-timer-cnt: fix ceiling write max value
>  counter: stm32-timer-cnt: Report count function when SLAVE_MODE_DISABLED
> 
> 
> For both the "stm32-lptimer-cnt" and "stm32-timer-cnt" drivers, I get a
> warning message and stack dump in "sysfs_emit" when reading the
> available functions from sysfs.
> I started to do some testing on v8 of this series last week. I didn't
> noticed that.
> 
> For both the "stm32-lptimer-cnt", there are 2 functions currently I get
> 1 stack dump. Only the "increase" function is printed correctly.
> 
> For the "stm32-timer-cnt", there are 4 functions currently, I get 3
> stack dumps. Only the "increase" function is printed correctly
> 
> Sample log for "stm32-timer-cnt:
> 
> root@stm32mp1:/sys/devices/platform/soc/44000000.timer/44000000.timer:counter/counter0#
> cat count0/function_available
> [ 4689.195506] ------------[ cut here ]------------
> [ 4689.198747] WARNING: CPU: 1 PID: 5841 at fs/sysfs/file.c:737
> sysfs_emit+0x88/0x94
> [ 4689.206233] invalid sysfs_emit: buf:f4a66208
> [ 4689.210553] Modules linked in: sha256_generic libsha256 sha256_arm
> cfg80211 panel_orisetech_otm8009a snd_soc_hdmi_codec
> snd_soc_stm32_sai_sub stm32_lptimers
> [ 4689.261444] CPU: 1 PID: 5841 Comm: cat Tainted: G        W
> 5.12.0-rc1 #534
> [ 4689.268999] Hardware name: STM32 (Device Tree Support)
> [ 4689.274166] [<c0310b38>] (unwind_backtrace) from [<c030b4ec>]
> (show_stack+0x10/0x14)
> [ 4689.281942] [<c030b4ec>] (show_stack) from [<c0fede70>]
> (dump_stack+0xc0/0xd4)
> [ 4689.289199] [<c0fede70>] (dump_stack) from [<c0345624>]
> (__warn+0xec/0x148)
> [ 4689.296194] [<c0345624>] (__warn) from [<c0fe9e90>]
> (warn_slowpath_fmt+0x98/0xbc)
> [ 4689.303714] [<c0fe9e90>] (warn_slowpath_fmt) from [<c0548ee0>]
> (sysfs_emit+0x88/0x94)
> [ 4689.311586] [<c0548ee0>] (sysfs_emit) from [<bf115de8>]
> (counter_comp_available_show+0x11c/0x1a4 [counter])
> [ 4689.321382] [<bf115de8>] (counter_comp_available_show [counter]) from
> [<c0a21b70>] (dev_attr_show+0x18/0x48)
> [ 4689.331263] [<c0a21b70>] (dev_attr_show) from [<c0549014>]
> (sysfs_kf_seq_show+0x88/0xf0)
> [ 4689.339394] [<c0549014>] (sysfs_kf_seq_show) from [<c04da6e8>]
> (seq_read_iter+0x1a4/0x554)
> [ 4689.347703] [<c04da6e8>] (seq_read_iter) from [<c04af6f0>]
> (vfs_read+0x1ac/0x2c4)
> [ 4689.355224] [<c04af6f0>] (vfs_read) from [<c04afc20>]
> (ksys_read+0x64/0xdc)
> [ 4689.362219] [<c04afc20>] (ksys_read) from [<c03000c0>]
> (ret_fast_syscall+0x0/0x58)
> [ 4689.369827] Exception stack(0xc7261fa8 to 0xc7261ff0)
> [ 4689.374906] 1fa0:                   00000000 00020000 00000003
> b6f35000 00020000 00000000
> [ 4689.383126] 1fc0: 00000000 00020000 b6f56ce0 00000003 00000003
> 00000000 00020000 00000000
> [ 4689.391344] 1fe0: 00000003 be8239a8 410bff27 4104c066
> ...
> 2 more stack dumps follow
> ...
> [ 4689.810479] ---[ end trace 59ed79949efe984c ]---
> increase
> 
> I get similar backtrace with other _available attributes:
> $ cat signal0_action_available
> $ cat signal1_action_available
> 
> Do you think I'm doing something wrong ?
> 
> I tested then "quadrature x4" on the timer driver... It seems all fine.
> 
> Best regards
> Fabrice
> 
> > +
> > +static ssize_t counter_comp_available_show(struct device *dev,
> > +					   struct device_attribute *attr,
> > +					   char *buf)
> > +{
> > +	const struct counter_attribute *const a = to_counter_attribute(attr);
> > +	const struct counter_count *const count = a->parent;
> > +	const struct counter_synapse *const synapse = a->comp.priv;
> > +	const struct counter_available *const avail = a->comp.priv;
> > +
> > +	switch (a->comp.type) {
> > +	case COUNTER_COMP_FUNCTION:
> > +		return enums_available_show(count->functions_list,
> > +					    count->num_functions,
> > +					    counter_function_str, buf);
> > +	case COUNTER_COMP_SYNAPSE_ACTION:
> > +		return enums_available_show(synapse->actions_list,
> > +					    synapse->num_actions,
> > +					    counter_synapse_action_str, buf);
> > +	case COUNTER_COMP_ENUM:
> > +		return strs_available_show(avail, buf);
> > +	case COUNTER_COMP_COUNT_MODE:
> > +		return enums_available_show(avail->enums, avail->num_items,
> > +					    counter_count_mode_str, buf);
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}

Hi Fabrice,

I can confirm that I'm hitting this regression as well with the
104-quad-8 driver. The warning seems to be caused by the
offset_in_page(buf) check in sysfs_emit(). It looks like the first loop
in enums_available_show() calls sysfs_emit() correctly, but subsequent
loops have an invalid buf offset.

The enums_available_show() callback is rather simple: call sysfs_emit()
for each enum string and increment buf by the length written each time.
I haven't modified this function since v8, so I am somewhat confused
about why the buf offset would be invalid here now. I wonder if there
has been a change somewhere else in the kernel that is causing
sysfs_emit() to now return an incorrect length.

William Breathitt Gray

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