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Subject[RFC][PATCH v2] efivars,efi-pstore: Hold off deletion of sysfs entry until the scan is completed
Change form v1
- Rebase to 3.12-rc2

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 read callback runnable without taking spinlok,
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.
Also, __efivar_entry_get() is removed because it was used in efi_pstore only.

[ 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@hds.com>
---
drivers/firmware/efi/efi-pstore.c | 145 +++++++++++++++++++++++++++++++++++---
drivers/firmware/efi/efivars.c | 3 +-
drivers/firmware/efi/vars.c | 39 +++-------
include/linux/efi.h | 4 +-
4 files changed, 151 insertions(+), 40 deletions(-)

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 5002d50..53001a5 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;
}
@@ -39,6 +37,23 @@ struct pstore_read_data {
char **buf;
};

+/**
+ * efi_pstore_read_func
+ * @entry: reading entry
+ * @data: data of the entry
+ *
+ * This function runs in non-atomic context.
+ *
+ * Also, it returns a size of NVRAM entry logged via efi_pstore_write().
+ * pstore in accordance with the returned value 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 int efi_pstore_read_func(struct efivar_entry *entry, void *data)
{
efi_guid_t vendor = LINUX_EFI_CRASH_GUID;
@@ -88,8 +103,9 @@ static int efi_pstore_read_func(struct efivar_entry *entry, void *data)
return 0;

entry->var.DataSize = 1024;
- __efivar_entry_get(entry, &entry->var.Attributes,
- &entry->var.DataSize, entry->var.Data);
+ efivar_entry_get(entry, &entry->var.Attributes,
+ &entry->var.DataSize, entry->var.Data);
+
size = entry->var.DataSize;

*cb_data->buf = kmemdup(entry->var.Data, size, GFP_KERNEL);
@@ -98,12 +114,114 @@ static int efi_pstore_read_func(struct efivar_entry *entry, void *data)
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;
+
+ /*
+ * Release a spin_lock because efi_pstore_read_func() should
+ * run in non-atomic context to allocate buffer dynamically.
+ */
+ efivar_entry_iter_end();
+}
+
+/**
+ * __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)
+{
+ /* Hold a spinlock to access efivar_entry safely. */
+ efivar_entry_iter_begin();
+ __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;
+}
+
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 +230,11 @@ 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);
+ efivar_entry_iter_begin();
+ size = efi_pstore_sysfs_entry_iter(&data,
+ (struct efivar_entry **)&psi->data);
+ efivar_entry_iter_end();
+ return size;
}

static int efi_pstore_write(enum pstore_type_id type,
@@ -184,9 +305,17 @@ 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;
}
@@ -216,7 +345,7 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
found = __efivar_entry_iter(efi_pstore_erase_func, &efivar_sysfs_list, &edata, &entry);
efivar_entry_iter_end();

- if (found)
+ if (found && !entry->scanning)
efivar_unregister(entry);

return 0;
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 8a7432a..831bc5c 100644
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -388,7 +388,8 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
if (err)
return err;

- efivar_unregister(entry);
+ if (!entry->scanning)
+ efivar_unregister(entry);

/* It's dead Jim.... */
return count;
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 391c67b..573ed92 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;
}
@@ -715,33 +723,6 @@ int efivar_entry_size(struct efivar_entry *entry, unsigned long *size)
EXPORT_SYMBOL_GPL(efivar_entry_size);

/**
- * __efivar_entry_get - call get_variable()
- * @entry: read data for this variable
- * @attributes: variable attributes
- * @size: size of @data buffer
- * @data: buffer to store variable data
- *
- * The caller MUST call efivar_entry_iter_begin() and
- * efivar_entry_iter_end() before and after the invocation of this
- * function, respectively.
- */
-int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
- unsigned long *size, void *data)
-{
- const struct efivar_operations *ops = __efivars->ops;
- efi_status_t status;
-
- WARN_ON(!spin_is_locked(&__efivars->lock));
-
- status = ops->get_variable(entry->var.VariableName,
- &entry->var.VendorGuid,
- attributes, size, data);
-
- return efi_status_to_err(status);
-}
-EXPORT_SYMBOL_GPL(__efivar_entry_get);
-
-/**
* efivar_entry_get - call get_variable()
* @entry: read data for this variable
* @attributes: variable attributes
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 5f8f176..1e3388e 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;
@@ -809,8 +811,6 @@ int __efivar_entry_delete(struct efivar_entry *entry);
int efivar_entry_delete(struct efivar_entry *entry);

int efivar_entry_size(struct efivar_entry *entry, unsigned long *size);
-int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
- unsigned long *size, void *data);
int efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
unsigned long *size, void *data);
int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
--
1.8.2.1


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