Re: [Patch v2] sysfs: add lockdep class support to s_active

[Xiaotian Feng <xtfeng@gmail.com>]

On Fri, Feb 5, 2010 at 2:42 PM, Amerigo Wang <amwang@redhat.com> wrote:
> Recently we met a lockdep warning from sysfs during s2ram or cpu hotplug.
> As reported by several people, it is something like:
>
> [ 6967.926563] ACPI: Preparing to enter system sleep state S3
> [ 6967.956156] Disabling non-boot CPUs ...
> [ 6967.970401]
> [ 6967.970408] =============================================
> [ 6967.970419] [ INFO: possible recursive locking detected ]
> [ 6967.970431] 2.6.33-rc2-git6 #27
> [ 6967.970439] ---------------------------------------------
> [ 6967.970450] pm-suspend/22147 is trying to acquire lock:
> [ 6967.970460]  (s_active){++++.+}, at: [<c10d2941>]
> sysfs_hash_and_remove+0x3d/0x4f
> [ 6967.970493]
> [ 6967.970497] but task is already holding lock:
> [ 6967.970506]  (s_active){++++.+}, at: [<c10d4110>]
> sysfs_get_active_two+0x16/0x36
> [...]
>
> Eric already provides a patch for this[1], but it still can't fix the
> problem. Based on his work and Peter's suggestion, I write this patch,
> hopefully we can fix the warning completely.
>
> This patch put sysfs s_active into two classes, one is for PM, the other
> is for the rest, so lockdep will distinguish them.

I think this patch does not hit the root cause, we have a similiar
warning which is not related with PM.
Reported by Nick when he's trying to switch evalator. It is
reproducable with "echo deadline >/sys/block/sdx/queue/scheduler"
while kernel is using cfq.

[ INFO: possible recursive locking detected ]
2.6.33-rc6 #1
---------------------------------------------
sh/889 is trying to acquire lock:
 (s_active){++++.+}, at: [<7820a975>] sysfs_addrm_finish+0x27/0x4e

but task is already holding lock:
 (s_active){++++.+}, at: [<7820ab82>] sysfs_get_active_two+0x18/0x3e

other info that might help us debug this:
4 locks held by sh/889:
 #0:  (&buffer->mutex){+.+.+.}, at: [<7820984e>] sysfs_write_file+0x20/0x99
 #1:  (s_active){++++.+}, at: [<7820ab82>] sysfs_get_active_two+0x18/0x3e
 #2:  (s_active){++++.+}, at: [<7820ab91>] sysfs_get_active_two+0x27/0x3e
 #3:  (&q->sysfs_lock){+.+.+.}, at: [<78289e95>] queue_attr_store+0x2e/0x68

stack backtrace:
Pid: 889, comm: sh Not tainted 2.6.33-rc6 #1
Call Trace:
 [<784a6966>] ? printk+0xf/0x11
 [<781752a1>] print_deadlock_bug+0x99/0xa3
 [<781753c6>] check_deadlock+0x11b/0x140
 [<781763e5>] validate_chain+0x4ec/0x4f9
 [<78176a68>] __lock_acquire+0x676/0x6cf
 [<78176b64>] lock_acquire+0xa3/0xbc
 [<7820a975>] ? sysfs_addrm_finish+0x27/0x4e
 [<7820a37a>] sysfs_deactivate+0x6c/0xa4
 [<7820a975>] ? sysfs_addrm_finish+0x27/0x4e
 [<7820a975>] sysfs_addrm_finish+0x27/0x4e
 [<7820aa3a>] sysfs_remove_dir+0x62/0x72
 [<7829d6dd>] kobject_del+0x11/0x32
 [<78283406>] __elv_unregister_queue+0x18/0x20
 [<78283c66>] elevator_switch+0x6d/0x11b
 [<78283d92>] elv_iosched_store+0x7e/0x9b
 [<78289eb8>] queue_attr_store+0x51/0x68
 [<78209894>] sysfs_write_file+0x66/0x99
 [<781cd460>] vfs_write+0x8a/0x108
 [<781cd578>] sys_write+0x3c/0x63
 [<78125b90>] sysenter_do_call+0x12/0x36

>
> 1. http://lkml.org/lkml/2010/1/10/282
>
>
> Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
> Reported-by: Miles Lane <miles.lane@gmail.com>
> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: WANG Cong <amwang@redhat.com>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>
>
> ---
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index 699f371..d7de269 100644
> --- a/fs/sysfs/dir.c
> +++ b/fs/sysfs/dir.c
> @@ -354,7 +354,6 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
>
>        atomic_set(&sd->s_count, 1);
>        atomic_set(&sd->s_active, 0);
> -       sysfs_dirent_init_lockdep(sd);
>
>        sd->s_name = name;
>        sd->s_mode = mode;
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index dc30d9e..97e397a 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -24,6 +24,8 @@
>
>  #include "sysfs.h"
>
> +static struct lock_class_key sysfs_classes[SYSFS_NR_CLASSES];
> +
>  /* used in crash dumps to help with debugging */
>  static char last_sysfs_file[PATH_MAX];
>  void sysfs_printk_last_file(void)
> @@ -504,11 +506,16 @@ int sysfs_add_file_mode(struct sysfs_dirent *dir_sd,
>        struct sysfs_addrm_cxt acxt;
>        struct sysfs_dirent *sd;
>        int rc;
> +       int class;
>
>        sd = sysfs_new_dirent(attr->name, mode, type);
>        if (!sd)
>                return -ENOMEM;
>        sd->s_attr.attr = (void *)attr;
> +       class = SYSFS_ATTR_NORMAL;
> +       if (sysfs_type(sd) == SYSFS_KOBJ_ATTR)
> +               class = sd->s_attr.attr->class;
> +       lockdep_set_class_and_name(sd, &sysfs_classes[class], "s_active");
>
>        sysfs_addrm_start(&acxt, dir_sd);
>        rc = sysfs_add_one(&acxt, sd);
> diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
> index cdd9377..dde4d73 100644
> --- a/fs/sysfs/sysfs.h
> +++ b/fs/sysfs/sysfs.h
> @@ -88,17 +88,6 @@ static inline unsigned int sysfs_type(struct sysfs_dirent *sd)
>        return sd->s_flags & SYSFS_TYPE_MASK;
>  }
>
> -#ifdef CONFIG_DEBUG_LOCK_ALLOC
> -#define sysfs_dirent_init_lockdep(sd)                          \
> -do {                                                           \
> -       static struct lock_class_key __key;                     \
> -                                                               \
> -       lockdep_init_map(&sd->dep_map, "s_active", &__key, 0);  \
> -} while(0)
> -#else
> -#define sysfs_dirent_init_lockdep(sd) do {} while(0)
> -#endif
> -
>  /*
>  * Context structure to be used while adding/removing nodes.
>  */
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index cfa8308..2b91b74 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -20,6 +20,12 @@
>  struct kobject;
>  struct module;
>
> +enum sysfs_attr_lock_class {
> +       SYSFS_ATTR_NORMAL,
> +       SYSFS_ATTR_PM_CONTROL,
> +       SYSFS_NR_CLASSES,
> +};
> +
>  /* FIXME
>  * The *owner field is no longer used.
>  * x86 tree has been cleaned up. The owner
> @@ -29,6 +35,7 @@ struct attribute {
>        const char              *name;
>        struct module           *owner;
>        mode_t                  mode;
> +       enum sysfs_attr_lock_class      class;
>  };
>
>  struct attribute_group {
> diff --git a/kernel/power/power.h b/kernel/power/power.h
> index 46c5a26..67a6fe7 100644
> --- a/kernel/power/power.h
> +++ b/kernel/power/power.h
> @@ -54,13 +54,14 @@ extern int hibernation_platform_enter(void);
>  extern int pfn_is_nosave(unsigned long);
>
>  #define power_attr(_name) \
> -static struct kobj_attribute _name##_attr = {  \
> -       .attr   = {                             \
> -               .name = __stringify(_name),     \
> -               .mode = 0644,                   \
> -       },                                      \
> -       .show   = _name##_show,                 \
> -       .store  = _name##_store,                \
> +static struct kobj_attribute _name##_attr = {          \
> +       .attr   = {                                     \
> +               .name = __stringify(_name),             \
> +               .mode = 0644,                           \
> +               .class = SYSFS_ATTR_PM_CONTROL,         \
> +       },                                              \
> +       .show   = _name##_show,                         \
> +       .store  = _name##_store,                        \
>  }
>
>  /* Preferred image size in bytes (default 500 MB) */
> --
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