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: Seiji Aguchi <seiji.aguchi@hds.com>
Tested-by: Madper Xie <cxie@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

3 files changed, 151 insertions, 16 deletions

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 5002d50e3781..6ce31e93da55 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, 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,
-                                   (struct efivar_entry **)&psi->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;
 }
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 933eb027d527..3dc248239197 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 391c67b182d9..b22659cccca4 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;
 }