[Mesa-dev] [PATCH] gallium/hud: bugfix: 68169 - Sensor extensions segfaults.

[Nicolai Hähnle]

On 12.10.2016 19:02, Steven Toth wrote:
> https://bugs.freedesktop.org/show_bug.cgi?id=98169
>
> Really a two part bug.
>
> 1. The recent extensions to the HUB framework were tested exclusively
> with glxgears/demo/head. None of these tools exercise the
> free_query_data() code path. When these codepaths were
> tested, thanks to Christoph, using heaven-unigine
> application, the sensors extension would segfault.
>
> 2. In a second case, same use case, extensions would
> return zero values for cpufrequency, network stats etc.
>
> On inspection, this was due to the 'unigine' application
> created the HUD contexts twice (two screens?). The
> extensions had never been tested in that configuration,
> and the free_query_data() calls were thus trigger.

The HUD is actually created per-context. Two general points that apply 
equally to all four parts of the patch:

Instead of open-coding the users variable, I'd prefer that you use the 
pipe_reference mechanism. This mechanism has the advantage that it 
already works in a multi-threaded setting, which brings me to the second 
point, which is:

Contexts can be created and destroyed simultaneously from multiple 
threads. You need to protect at least the globals with a mutex, i.e. in 
the find_*_by_name and free_query_data.

You probably need to protect some of the query functions with a mutex as 
well. The general rule of thumb is that functions associated to a 
pipe_context can only be called from one thread at a time; i.e., the 
graph's callback function (like query_dsi_load) is only called from one 
thread at a time _for one particular graph_. However, since you're 
sharing the underlying data between graphs in multiple contexts, you 
need a mutex e.g. in query_dsi_load when accessing the dsi members.

At least you need to think through the implications of what happens here...

It may actually be cleaner and simpler to just get rid of the sharing of 
underlying structures.

Thanks for looking into this!

Cheers,
Nicolai

> This patchset ensures that globally allocated
> mechanisms for collecting and exposing various
> disk, network, cpu frequency and sensors statistics
> are retained correctly across multiple uses, and
> free'd when no more callers require them.
>
> Patchset was regression tested again with Unigine,
> glxgears and glxdemo.
>
> Tested-By: Christoph Haag <haagch at frickel.club>
> Signed-off-by: Steven Toth <stoth at kernellabs.com>
> ---
>  src/gallium/auxiliary/hud/hud_cpufreq.c      |  8 ++++++--
>  src/gallium/auxiliary/hud/hud_diskstat.c     | 10 +++++++---
>  src/gallium/auxiliary/hud/hud_nic.c          |  8 ++++++--
>  src/gallium/auxiliary/hud/hud_sensors_temp.c | 18 +++++++++++++-----
>  4 files changed, 32 insertions(+), 12 deletions(-)
>
> diff --git a/src/gallium/auxiliary/hud/hud_cpufreq.c b/src/gallium/auxiliary/hud/hud_cpufreq.c
> index 4501bbb..39bdcb0 100644
> --- a/src/gallium/auxiliary/hud/hud_cpufreq.c
> +++ b/src/gallium/auxiliary/hud/hud_cpufreq.c
> @@ -57,6 +57,7 @@ struct cpufreq_info
>     char sysfs_filename[128];
>     uint64_t KHz;
>     uint64_t last_time;
> +   int users;
>  };
>
>  static int gcpufreq_count = 0;
> @@ -116,8 +117,10 @@ static void
>  free_query_data(void *p)
>  {
>     struct cpufreq_info *cfi = (struct cpufreq_info *)p;
> -   list_del(&cfi->list);
> -   FREE(cfi);
> +   if (--cfi->users == 0) {
> +      list_del(&cfi->list);
> +      FREE(cfi);
> +   }
>  }
>
>  /**
> @@ -159,6 +162,7 @@ hud_cpufreq_graph_install(struct hud_pane *pane, int cpu_index,
>        return;
>     }
>
> +   cfi->users++;
>     gr->query_data = cfi;
>     gr->query_new_value = query_cfi_load;
>
> diff --git a/src/gallium/auxiliary/hud/hud_diskstat.c b/src/gallium/auxiliary/hud/hud_diskstat.c
> index b248baf..000d6b3 100644
> --- a/src/gallium/auxiliary/hud/hud_diskstat.c
> +++ b/src/gallium/auxiliary/hud/hud_diskstat.c
> @@ -73,6 +73,7 @@ struct diskstat_info
>     char sysfs_filename[128];
>     uint64_t last_time;
>     struct stat_s last_stat;
> +   int users;
>  };
>
>  /* TODO: We don't handle dynamic block device / partition
> @@ -165,9 +166,11 @@ query_dsi_load(struct hud_graph *gr)
>  static void
>  free_query_data(void *p)
>  {
> -   struct diskstat_info *nic = (struct diskstat_info *) p;
> -   list_del(&nic->list);
> -   FREE(nic);
> +   struct diskstat_info *dsi = (struct diskstat_info *) p;
> +   if (--dsi->users == 0) {
> +      list_del(&dsi->list);
> +      FREE(dsi);
> +   }
>  }
>
>  /**
> @@ -205,6 +208,7 @@ hud_diskstat_graph_install(struct hud_pane *pane, const char *dev_name,
>     else
>        return;
>
> +   dsi->users++;
>     gr->query_data = dsi;
>     gr->query_new_value = query_dsi_load;
>
> diff --git a/src/gallium/auxiliary/hud/hud_nic.c b/src/gallium/auxiliary/hud/hud_nic.c
> index fb6b8c0..e3f5910 100644
> --- a/src/gallium/auxiliary/hud/hud_nic.c
> +++ b/src/gallium/auxiliary/hud/hud_nic.c
> @@ -59,6 +59,7 @@ struct nic_info
>     char throughput_filename[128];
>     uint64_t last_time;
>     uint64_t last_nic_bytes;
> +   int users;
>  };
>
>  /* TODO: We don't handle dynamic NIC arrival or removal.
> @@ -238,8 +239,10 @@ static void
>  free_query_data(void *p)
>  {
>     struct nic_info *nic = (struct nic_info *) p;
> -   list_del(&nic->list);
> -   FREE(nic);
> +   if (--nic->users == 0) {
> +      list_del(&nic->list);
> +      FREE(nic);
> +   }
>  }
>
>  /**
> @@ -281,6 +284,7 @@ hud_nic_graph_install(struct hud_pane *pane, const char *nic_name,
>     else
>        return;
>
> +   nic->users++;
>     gr->query_data = nic;
>     gr->query_new_value = query_nic_load;
>
> diff --git a/src/gallium/auxiliary/hud/hud_sensors_temp.c b/src/gallium/auxiliary/hud/hud_sensors_temp.c
> index e41b847..c6f7d5b 100644
> --- a/src/gallium/auxiliary/hud/hud_sensors_temp.c
> +++ b/src/gallium/auxiliary/hud/hud_sensors_temp.c
> @@ -68,6 +68,7 @@ struct sensors_temp_info
>     sensors_chip_name *chip;
>     const sensors_feature *feature;
>     double current, min, max, critical;
> +   int users;
>  };
>
>  static double
> @@ -193,11 +194,17 @@ static void
>  free_query_data(void *p)
>  {
>     struct sensors_temp_info *sti = (struct sensors_temp_info *) p;
> -   list_del(&sti->list);
> -   if (sti->chip)
> -      sensors_free_chip_name(sti->chip);
> -   FREE(sti);
> -   sensors_cleanup();
> +   if (--sti->users == 0) {
> +      list_del(&sti->list);
> +      gsensors_temp_count--;
> +      if (sti->chip)
> +         sensors_free_chip_name(sti->chip);
> +      FREE(sti);
> +   }
> +
> +   /* Destroy sensor singleton when after all refs released. */
> +   if (!gsensors_temp_count)
> +      sensors_cleanup();
>  }
>
>  /**
> @@ -234,6 +241,7 @@ hud_sensors_temp_graph_install(struct hud_pane *pane, const char *dev_name,
>             sti->mode == SENSORS_POWER_CURRENT ? "Pow" :
>             sti->mode == SENSORS_TEMP_CRITICAL ? "Crit" : "Unkn");
>
> +   sti->users++;
>     gr->query_data = sti;
>     gr->query_new_value = query_sti_load;
>
>