Message-ID: <878uxssarf.fsf@redhat.com>
Date:	Thu, 17 Oct 2013 13:54:12 +0800
From:	Madper Xie <cxie@...hat.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	matt.fleming@...el.com, tony.luck@...el.com,
	tomoki.sekiyama@....com, dle-develop@...ts.sourceforge.net
Subject: Re: [PATCH v3] efivars,efi-pstore: Hold off deletion of sysfs entry until, the scan is completed

Howdy Seiji,
  I failed appily this patch to both 3.12-rc2 and 3.12-rc4. Could you
  please let me know which is the right tree for this patch?

  Thanks,
  Madper.
seiji.aguchi@....com writes:

> Change from v2:
> - Move dynamic memory allocation to efi_pstore_read() before holding
>   efivars->lock to protect entry->var.Data.
> - Access to entry->scanning while holding efivars->lock.
> - Move a comment about a returned value from efi_pstore_read_func() to
>   efi_pstore_read() because "size < 0" case may happen in efi_pstore_read().
>
> Currently, when mounting pstore file system, a read callback of efi_pstore
> driver runs mutiple times as below.
>
> - In the first read callback, scan efivar_sysfs_list from head and pass
>   a kmsg buffer of a entry to an upper pstore layer.
> - In the second read callback, rescan efivar_sysfs_list from the entry and pass
>   another kmsg buffer to it.
> - Repeat the scan and pass until the end of efivar_sysfs_list.
>
> In this process, an entry is read across the multiple read function calls.
> To avoid race between the read and erasion, the whole process above is
> protected by a spinlock, holding in open() and releasing in close().
>
> At the same time, kmemdup() is called to pass the buffer to pstore filesystem
> during it.
> And then, it causes a following lockdep warning.
>
> To make the dynamic memory allocation runnable without taking spinlock,
> holding off a deletion of sysfs entry if it happens while scanning it
> via efi_pstore, and deleting it after the scan is completed.
>
> To implement it, this patch introduces two flags, scanning and deleting,
> to efivar_entry.
>
> [    1.143710] ------------[ cut here ]------------
> [    1.144058] WARNING: CPU: 1 PID: 1 at kernel/lockdep.c:2740
> lockdep_trace_alloc+0x104/0x110()
> [    1.144058] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> [    1.144058] Modules linked in:
>
> [    1.144058] CPU: 1 PID: 1 Comm: systemd Not tainted 3.11.0-rc5 #2
> [    1.144058]  0000000000000009 ffff8800797e9ae0 ffffffff816614a5
> ffff8800797e9b28
> [    1.144058]  ffff8800797e9b18 ffffffff8105510d 0000000000000080
> 0000000000000046
> [    1.144058]  00000000000000d0 00000000000003af ffffffff81ccd0c0
> ffff8800797e9b78
> [    1.144058] Call Trace:
> [    1.144058]  [<ffffffff816614a5>] dump_stack+0x54/0x74
> [    1.144058]  [<ffffffff8105510d>] warn_slowpath_common+0x7d/0xa0
> [    1.144058]  [<ffffffff8105517c>] warn_slowpath_fmt+0x4c/0x50
> [    1.144058]  [<ffffffff8131290f>] ? vsscanf+0x57f/0x7b0
> [    1.144058]  [<ffffffff810bbd74>] lockdep_trace_alloc+0x104/0x110
> [    1.144058]  [<ffffffff81192da0>] __kmalloc_track_caller+0x50/0x280
> [    1.144058]  [<ffffffff815147bb>] ?
> efi_pstore_read_func.part.1+0x12b/0x170
> [    1.144058]  [<ffffffff8115b260>] kmemdup+0x20/0x50
> [    1.144058]  [<ffffffff815147bb>] efi_pstore_read_func.part.1+0x12b/0x170
> [    1.144058]  [<ffffffff81514800>] ?
> efi_pstore_read_func.part.1+0x170/0x170
> [    1.144058]  [<ffffffff815148b4>] efi_pstore_read_func+0xb4/0xe0
> [    1.144058]  [<ffffffff81512b7b>] __efivar_entry_iter+0xfb/0x120
> [    1.144058]  [<ffffffff8151428f>] efi_pstore_read+0x3f/0x50
> [    1.144058]  [<ffffffff8128d7ba>] pstore_get_records+0x9a/0x150
> [    1.158207]  [<ffffffff812af25c>] ? selinux_d_instantiate+0x1c/0x20
> [    1.158207]  [<ffffffff8128ce30>] ? parse_options+0x80/0x80
> [    1.158207]  [<ffffffff8128ced5>] pstore_fill_super+0xa5/0xc0
> [    1.158207]  [<ffffffff811ae7d2>] mount_single+0xa2/0xd0
> [    1.158207]  [<ffffffff8128ccf8>] pstore_mount+0x18/0x20
> [    1.158207]  [<ffffffff811ae8b9>] mount_fs+0x39/0x1b0
> [    1.158207]  [<ffffffff81160550>] ? __alloc_percpu+0x10/0x20
> [    1.158207]  [<ffffffff811c9493>] vfs_kern_mount+0x63/0xf0
> [    1.158207]  [<ffffffff811cbb0e>] do_mount+0x23e/0xa20
> [    1.158207]  [<ffffffff8115b51b>] ? strndup_user+0x4b/0xf0
> [    1.158207]  [<ffffffff811cc373>] SyS_mount+0x83/0xc0
> [    1.158207]  [<ffffffff81673cc2>] system_call_fastpath+0x16/0x1b
> [    1.158207] ---[ end trace 61981bc62de9f6f4 ]---
>
> Signed-off-by: Seiji Aguchi <seiji.aguchi@....com>
> ---
>  drivers/firmware/efi/efi-pstore.c | 143 +++++++++++++++++++++++++++++++++++---
>  drivers/firmware/efi/efivars.c    |  12 ++--
>  drivers/firmware/efi/vars.c       |  12 +++-
>  include/linux/efi.h               |   2 +
>  4 files changed, 153 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
> index 5002d50..ebd5dbc 100644
> --- a/drivers/firmware/efi/efi-pstore.c
> +++ b/drivers/firmware/efi/efi-pstore.c
> @@ -18,14 +18,12 @@ module_param_named(pstore_disable, efivars_pstore_disable, bool, 0644);
>  
>  static int efi_pstore_open(struct pstore_info *psi)
>  {
> -	efivar_entry_iter_begin();
>  	psi->data = NULL;
>  	return 0;
>  }
>  
>  static int efi_pstore_close(struct pstore_info *psi)
>  {
> -	efivar_entry_iter_end();
>  	psi->data = NULL;
>  	return 0;
>  }
> @@ -91,19 +89,125 @@ static int efi_pstore_read_func(struct efivar_entry *entry, void *data)
>  	__efivar_entry_get(entry, &entry->var.Attributes,
>  			   &entry->var.DataSize, entry->var.Data);
>  	size = entry->var.DataSize;
> +	memcpy(*cb_data->buf, entry->var.Data, (size_t)min_t(unsigned long,
> +							     1024, size));
>  
> -	*cb_data->buf = kmemdup(entry->var.Data, size, GFP_KERNEL);
> -	if (*cb_data->buf == NULL)
> -		return -ENOMEM;
>  	return size;
>  }
>  
> +/**
> + * efi_pstore_scan_sysfs_enter
> + * @entry: scanning entry
> + * @next: next entry
> + * @head: list head
> + */
> +static void efi_pstore_scan_sysfs_enter(struct efivar_entry *pos,
> +					struct efivar_entry *next,
> +					struct list_head *head)
> +{
> +	pos->scanning = true;
> +	if (&next->list != head)
> +		next->scanning = true;
> +}
> +
> +/**
> + * __efi_pstore_scan_sysfs_exit
> + * @entry: deleting entry
> + * @turn_off_scanning: Check if a scanning flag should be turned off
> + */
> +static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
> +						bool turn_off_scanning)
> +{
> +	if (entry->deleting) {
> +		list_del(&entry->list);
> +		efivar_entry_iter_end();
> +		efivar_unregister(entry);
> +		efivar_entry_iter_begin();
> +	} else if (turn_off_scanning)
> +		entry->scanning = false;
> +}
> +
> +/**
> + * efi_pstore_scan_sysfs_exit
> + * @pos: scanning entry
> + * @next: next entry
> + * @head: list head
> + * @stop: a flag checking if scanning will stop
> + */
> +static void efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
> +				       struct efivar_entry *next,
> +				       struct list_head *head, bool stop)
> +{
> +	__efi_pstore_scan_sysfs_exit(pos, true);
> +	if (stop)
> +		__efi_pstore_scan_sysfs_exit(next, &next->list != head);
> +}
> +
> +/**
> + * efi_pstore_sysfs_entry_iter
> + *
> + * @data: function-specific data to pass to callback
> + * @pos: entry to begin iterating from
> + *
> + * You MUST call efivar_enter_iter_begin() before this function, and
> + * efivar_entry_iter_end() afterwards.
> + *
> + * It is possible to begin iteration from an arbitrary entry within
> + * the list by passing @pos. @pos is updated on return to point to
> + * the next entry of the last one passed to efi_pstore_read_func().
> + * To begin iterating from the beginning of the list @pos must be %NULL.
> + */
> +static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
> +{
> +	struct efivar_entry *entry, *n;
> +	struct list_head *head = &efivar_sysfs_list;
> +	int size = 0;
> +
> +	if (!*pos) {
> +		list_for_each_entry_safe(entry, n, head, list) {
> +			efi_pstore_scan_sysfs_enter(entry, n, head);
> +
> +			size = efi_pstore_read_func(entry, data);
> +			efi_pstore_scan_sysfs_exit(entry, n, head, size < 0);
> +			if (size)
> +				break;
> +		}
> +		*pos = n;
> +		return size;
> +	}
> +
> +	list_for_each_entry_safe_from((*pos), n, head, list) {
> +		efi_pstore_scan_sysfs_enter((*pos), n, head);
> +
> +		size = efi_pstore_read_func((*pos), data);
> +		efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
> +		if (size)
> +			break;
> +	}
> +	*pos = n;
> +	return size;
> +}
> +
> +/**
> + * efi_pstore_read
> + *
> + * This function returns a size of NVRAM entry logged via efi_pstore_write().
> + * The meaning and behavior of efi_pstore/pstore are as below.
> + *
> + * size > 0: Got data of an entry logged via efi_pstore_write() successfully,
> + *           and pstore filesystem will continue reading subsequent entries.
> + * size == 0: Entry was not logged via efi_pstore_write(),
> + *            and efi_pstore driver will continue reading subsequent entries.
> + * size < 0: Failed to get data of entry logging via efi_pstore_write(),
> + *           and pstore will stop reading entry.
> + */
>  static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
>  			       int *count, struct timespec *timespec,
>  			       char **buf, bool *compressed,
>  			       struct pstore_info *psi)
>  {
>  	struct pstore_read_data data;
> +	ssize_t size;
>  
>  	data.id = id;
>  	data.type = type;
> @@ -112,8 +216,17 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
>  	data.compressed = compressed;
>  	data.buf = buf;
>  
> -	return __efivar_entry_iter(efi_pstore_read_func, &efivar_sysfs_list, &data,
> -				   (struct efivar_entry **)&psi->data);
> +	*data.buf = kzalloc(1024, GFP_KERNEL);
> +	if (!*data.buf)
> +		return -ENOMEM;
> +
> +	efivar_entry_iter_begin();
> +	size = efi_pstore_sysfs_entry_iter(&data,
> +					   (struct efivar_entry **)&psi->data);
> +	efivar_entry_iter_end();
> +	if (size <= 0)
> +		kfree(*data.buf);
> +	return size;
>  }
>  
>  static int efi_pstore_write(enum pstore_type_id type,
> @@ -184,9 +297,17 @@ static int efi_pstore_erase_func(struct efivar_entry *entry, void *data)
>  			return 0;
>  	}
>  
> +	if (entry->scanning) {
> +		/*
> +		 * Skip deletion because this entry will be deleted
> +		 * after scanning is completed.
> +		 */
> +		entry->deleting = true;
> +	} else
> +		list_del(&entry->list);
> +
>  	/* found */
>  	__efivar_entry_delete(entry);
> -	list_del(&entry->list);
>  
>  	return 1;
>  }
> @@ -214,10 +335,12 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
>  
>  	efivar_entry_iter_begin();
>  	found = __efivar_entry_iter(efi_pstore_erase_func, &efivar_sysfs_list, &edata, &entry);
> -	efivar_entry_iter_end();
>  
> -	if (found)
> +	if (found && !entry->scanning) {
> +		efivar_entry_iter_end();
>  		efivar_unregister(entry);
> +	} else
> +		efivar_entry_iter_end();
>  
>  	return 0;
>  }
> diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
> index 8a7432a..8c5a61a 100644
> --- a/drivers/firmware/efi/efivars.c
> +++ b/drivers/firmware/efi/efivars.c
> @@ -383,12 +383,16 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
>  	else if (__efivar_entry_delete(entry))
>  		err = -EIO;
>  
> -	efivar_entry_iter_end();
> -
> -	if (err)
> +	if (err) {
> +		efivar_entry_iter_end();
>  		return err;
> +	}
>  
> -	efivar_unregister(entry);
> +	if (!entry->scanning) {
> +		efivar_entry_iter_end();
> +		efivar_unregister(entry);
> +	} else
> +		efivar_entry_iter_end();
>  
>  	/* It's dead Jim.... */
>  	return count;
> diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> index 391c67b..b22659c 100644
> --- a/drivers/firmware/efi/vars.c
> +++ b/drivers/firmware/efi/vars.c
> @@ -683,8 +683,16 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
>  	if (!found)
>  		return NULL;
>  
> -	if (remove)
> -		list_del(&entry->list);
> +	if (remove) {
> +		if (entry->scanning) {
> +			/*
> +			 * The entry will be deleted
> +			 * after scanning is completed.
> +			 */
> +			entry->deleting = true;
> +		} else
> +			list_del(&entry->list);
> +	}
>  
>  	return entry;
>  }
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 5f8f176..04088fb 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -782,6 +782,8 @@ struct efivar_entry {
>  	struct efi_variable var;
>  	struct list_head list;
>  	struct kobject kobj;
> +	bool scanning;
> +	bool deleting;
>  };
>  
>  extern struct list_head efivar_sysfs_list;


-- 
Best,
Madper Xie.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists