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Commit e0d59733 authored by Seiji Aguchi's avatar Seiji Aguchi Committed by Matt Fleming
Browse files

efivars, efi-pstore: Hold off deletion of sysfs entry until the scan is completed 



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.

On the code basis, it seems that all the scanning and deleting logic is
not needed because __efivars->lock are not dropped when reading from the
EFI variable store.

But, the scanning and deleting logic is still needed because an
efi-pstore and a pstore filesystem works as follows.

In case an entry(A) is found, the pointer is saved to psi->data.  And
efi_pstore_read() passes the entry(A) to a pstore filesystem by
releasing  __efivars->lock.

And then, the pstore filesystem calls efi_pstore_read() again and the
same entry(A), which is saved to psi->data, is used for resuming to scan
a sysfs-list.

So, to protect the entry(A), the logic is needed.

[    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: default avatarSeiji Aguchi <seiji.aguchi@hds.com>
Tested-by: default avatarMadper Xie <cxie@redhat.com>
Cc: stable@kernel.org
Signed-off-by: default avatarMatt Fleming <matt.fleming@intel.com>
parent 6ce4eac1

drivers/firmware/efi/efi-pstore.c

+133 −10
Original line number Diff line number Diff line
@@ -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, EFIVARS_DATA_SIZE_MAX, 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,

	*data.buf = kzalloc(EFIVARS_DATA_SIZE_MAX, 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;

}

drivers/firmware/efi/efivars.c

+8 −4
Original line number Diff line number Diff line
@@ -383,12 +383,16 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj, 
	else if (__efivar_entry_delete(entry))

		err = -EIO;



	if (err) {

		efivar_entry_iter_end();



	if (err)

		return err;

	}



	if (!entry->scanning) {

		efivar_entry_iter_end();

		efivar_unregister(entry);

	} else

		efivar_entry_iter_end();



	/* It's dead Jim.... */

	return count;

drivers/firmware/efi/vars.c

+10 −2
Original line number Diff line number Diff line
@@ -683,8 +683,16 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid, 
	if (!found)

		return NULL;



	if (remove)

	if (remove) {

		if (entry->scanning) {

			/*

			 * The entry will be deleted

			 * after scanning is completed.

			 */

			entry->deleting = true;

		} else

			list_del(&entry->list);

	}



	return entry;

}

include/linux/efi.h

+4 −0
Original line number Diff line number Diff line
@@ -801,6 +801,8 @@ struct efivar_entry { 
	struct efi_variable var;

	struct list_head list;

	struct kobject kobj;

	bool scanning;

	bool deleting;

};
@@ -866,6 +868,8 @@ void efivar_run_worker(void); 
#if defined(CONFIG_EFI_VARS) || defined(CONFIG_EFI_VARS_MODULE)

int efivars_sysfs_init(void);



#define EFIVARS_DATA_SIZE_MAX 1024



#endif /* CONFIG_EFI_VARS */



#endif /* _LINUX_EFI_H */