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Date: Fri, 17 Aug 2012 13:18:04 -0700
From: Mike Waychison <mikew@...gle.com>
To: Seiji Aguchi <seiji.aguchi@....com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Luck, Tony (tony.luck@...el.com)" <tony.luck@...el.com>,
"Matthew Garrett (mjg@...hat.com)" <mjg@...hat.com>,
"dzickus@...hat.com" <dzickus@...hat.com>,
"dle-develop@...ts.sourceforge.net"
<dle-develop@...ts.sourceforge.net>,
Satoru Moriya <satoru.moriya@....com>
Subject: Re: [RFC][PATCH 1/2] efivars: Disable external interrupt while
holding efivars->lock
On Fri, Aug 17, 2012 at 12:42 PM, Seiji Aguchi <seiji.aguchi@....com> wrote:
> [Problem]
> Currently, efivars doesn't disable interrupt while taking efivars->lock.
> So, there is a risk to be deadlocking in a write callback of efi_pstore
> if kernel panics in interrupt context while taking efivars->lock.
>
> [Patch Description]
> This patch disables an external interruption while holding efivars->lock by
> replacing spin_lock/spin_unlock with spin_lock_irqsave/spin_unlock_irqrestore.
>
> As for spin_locks in open/close callbacks of efi_pstore, they moved to a read callback
> to pass a flags argument to spin_lock_irqsave/spin_unlock_irqrestore.
This isn't necessary (nor desirable). If the API here is that we get
called from process context for ->open and ->close(), just use the
spin_lock_irq and spin_unlock_irq variants for these paths (avoiding
the need to remove the lock acquire in ->open and ->close.
>
> Even if spin_locks in open/close callbacks are erased, a whole process of open/read/close
> is still serialized by psinfo->read_mutex which is taken in a pstore layer.
>
> Also, initialization of efivars->walk_entry moved to a read callback to protect list_first_entry()
> with efivars->lock. And some comments about efivars->walk_entry are added to avoid using it
> without taking psinfo->read_mutex.
>
> Signed-off-by: Seiji Aguchi <seiji.aguchi@....com>
> ---
> drivers/firmware/efivars.c | 66 ++++++++++++++++++++++++++-----------------
> include/linux/efi.h | 3 ++
> 2 files changed, 43 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
> index 47408e8..b6a813e 100644
> --- a/drivers/firmware/efivars.c
> +++ b/drivers/firmware/efivars.c
> @@ -393,10 +393,11 @@ static efi_status_t
> get_var_data(struct efivars *efivars, struct efi_variable *var)
> {
> efi_status_t status;
> + unsigned long flags;
>
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
> status = get_var_data_locked(efivars, var);
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
>
> if (status != EFI_SUCCESS) {
> printk(KERN_WARNING "efivars: get_variable() failed 0x%lx!\n",
> @@ -488,6 +489,7 @@ efivar_store_raw(struct efivar_entry *entry, const char *buf, size_t count)
> struct efi_variable *new_var, *var = &entry->var;
> struct efivars *efivars = entry->efivars;
> efi_status_t status = EFI_NOT_FOUND;
> + unsigned long flags;
>
> if (count != sizeof(struct efi_variable))
> return -EINVAL;
> @@ -514,14 +516,14 @@ efivar_store_raw(struct efivar_entry *entry, const char *buf, size_t count)
> return -EINVAL;
> }
>
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
> status = efivars->ops->set_variable(new_var->VariableName,
> &new_var->VendorGuid,
> new_var->Attributes,
> new_var->DataSize,
> new_var->Data);
>
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
>
> if (status != EFI_SUCCESS) {
> printk(KERN_WARNING "efivars: set_variable() failed: status=%lx\n",
> @@ -630,19 +632,11 @@ efivar_unregister(struct efivar_entry *var)
>
> static int efi_pstore_open(struct pstore_info *psi)
> {
> - struct efivars *efivars = psi->data;
> -
> - spin_lock(&efivars->lock);
> - efivars->walk_entry = list_first_entry(&efivars->list,
> - struct efivar_entry, list);
> return 0;
> }
>
> static int efi_pstore_close(struct pstore_info *psi)
> {
> - struct efivars *efivars = psi->data;
> -
> - spin_unlock(&efivars->lock);
> return 0;
> }
>
> @@ -656,6 +650,17 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
> int i;
> unsigned int part, size;
> unsigned long time;
> + static unsigned long flags;
> +
> + /*
> + * efivars->walk_entry is protected by pstore_info.read_mutex
> + */
> + if (!efivars->walk_entry) {
> + spin_lock_irqsave(&efivars->lock, flags);
> + efivars->walk_entry = list_first_entry(&efivars->list,
> + struct efivar_entry,
> + list);
> + }
>
> while (&efivars->walk_entry->list != &efivars->list) {
> if (!efi_guidcmp(efivars->walk_entry->var.VendorGuid,
> @@ -682,6 +687,10 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
> efivars->walk_entry = list_entry(efivars->walk_entry->list.next,
> struct efivar_entry, list);
> }
> +
> + efivars->walk_entry = NULL;
> + spin_unlock_irqrestore(&efivars->lock, flags);
This doesn't look right. Why are we only conditionally locking above?
Having the iterator state live in efivars->walk_entry seems wrong.
Any reason we shouldn't move this into pstore_info (a void *private
would do).
> +
> return 0;
> }
>
> @@ -696,11 +705,12 @@ static int efi_pstore_write(enum pstore_type_id type,
> struct efivars *efivars = psi->data;
> struct efivar_entry *entry, *found = NULL;
> int i, ret = 0;
> + unsigned long flags;
>
> sprintf(stub_name, "dump-type%u-%u-", type, part);
> sprintf(name, "%s%lu", stub_name, get_seconds());
>
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
>
> for (i = 0; i < DUMP_NAME_LEN; i++)
> efi_name[i] = stub_name[i];
> @@ -738,7 +748,7 @@ static int efi_pstore_write(enum pstore_type_id type,
> efivars->ops->set_variable(efi_name, &vendor, PSTORE_EFI_ATTRIBUTES,
> size, psi->buf);
>
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
>
> if (found)
> efivar_unregister(found);
> @@ -812,6 +822,7 @@ static ssize_t efivar_create(struct file *filp, struct kobject *kobj,
> unsigned long strsize1, strsize2;
> efi_status_t status = EFI_NOT_FOUND;
> int found = 0;
> + unsigned long flags;
>
> if (!capable(CAP_SYS_ADMIN))
> return -EACCES;
> @@ -822,7 +833,7 @@ static ssize_t efivar_create(struct file *filp, struct kobject *kobj,
> return -EINVAL;
> }
>
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
>
> /*
> * Does this variable already exist?
> @@ -840,7 +851,7 @@ static ssize_t efivar_create(struct file *filp, struct kobject *kobj,
> }
> }
> if (found) {
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
> return -EINVAL;
> }
>
> @@ -854,10 +865,10 @@ static ssize_t efivar_create(struct file *filp, struct kobject *kobj,
> if (status != EFI_SUCCESS) {
> printk(KERN_WARNING "efivars: set_variable() failed: status=%lx\n",
> status);
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
> return -EIO;
> }
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
>
> /* Create the entry in sysfs. Locking is not required here */
> status = efivar_create_sysfs_entry(efivars,
> @@ -881,11 +892,12 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
> unsigned long strsize1, strsize2;
> efi_status_t status = EFI_NOT_FOUND;
> int found = 0;
> + unsigned long flags;
>
> if (!capable(CAP_SYS_ADMIN))
> return -EACCES;
>
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
>
> /*
> * Does this variable already exist?
> @@ -903,7 +915,7 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
> }
> }
> if (!found) {
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
> return -EINVAL;
> }
> /* force the Attributes/DataSize to 0 to ensure deletion */
> @@ -919,12 +931,12 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
> if (status != EFI_SUCCESS) {
> printk(KERN_WARNING "efivars: set_variable() failed: status=%lx\n",
> status);
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
> return -EIO;
> }
> list_del(&search_efivar->list);
> /* We need to release this lock before unregistering. */
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
> efivar_unregister(search_efivar);
>
> /* It's dead Jim.... */
> @@ -993,6 +1005,7 @@ efivar_create_sysfs_entry(struct efivars *efivars,
> int i, short_name_size = variable_name_size / sizeof(efi_char16_t) + 38;
> char *short_name;
> struct efivar_entry *new_efivar;
> + unsigned long flags;
>
> short_name = kzalloc(short_name_size + 1, GFP_KERNEL);
> new_efivar = kzalloc(sizeof(struct efivar_entry), GFP_KERNEL);
> @@ -1032,9 +1045,9 @@ efivar_create_sysfs_entry(struct efivars *efivars,
> kfree(short_name);
> short_name = NULL;
>
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
> list_add(&new_efivar->list, &efivars->list);
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
>
> return 0;
> }
> @@ -1101,11 +1114,12 @@ out_free:
> void unregister_efivars(struct efivars *efivars)
> {
> struct efivar_entry *entry, *n;
> + unsigned long flags;
>
> list_for_each_entry_safe(entry, n, &efivars->list, list) {
> - spin_lock(&efivars->lock);
> + spin_lock_irqsave(&efivars->lock, flags);
> list_del(&entry->list);
> - spin_unlock(&efivars->lock);
> + spin_unlock_irqrestore(&efivars->lock, flags);
> efivar_unregister(entry);
> }
> if (efivars->new_var)
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 103adc6..f1f5703 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -649,6 +649,9 @@ struct efivars {
> struct kset *kset;
> struct bin_attribute *new_var, *del_var;
> const struct efivar_operations *ops;
> + /*
> + * walk_entry is protected by pstore_info.read_mutex
> + */
> struct efivar_entry *walk_entry;
> struct pstore_info efi_pstore_info;
> };
> -- 1.7.1
--
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