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Date: Fri, 4 Oct 2013 15:46:50 +0000
From: Seiji Aguchi <seiji.aguchi@....com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
"tony.luck@...el.com" <tony.luck@...el.com>,
"matt.fleming@...el.com" <matt.fleming@...el.com>
CC: "dle-develop@...ts.sourceforge.net"
<dle-develop@...ts.sourceforge.net>,
Tomoki Sekiyama <tomoki.sekiyama@....com>
Subject: RE: [RFC][PATCH v2] efivars,efi-pstore: Hold off deletion of sysfs
entry until the scan is completed
Are there anyone who can review this bugfix?
Seiji
> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Seiji Aguchi
> Sent: Friday, September 27, 2013 4:24 PM
> To: linux-kernel@...r.kernel.org; linux-efi@...r.kernel.org; tony.luck@...el.com; matt.fleming@...el.com
> Cc: dle-develop@...ts.sourceforge.net; Tomoki Sekiyama
> 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@....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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