scsiback_free_translation_entry() shouldn't be called under spinlock,
as it can sleep.
This requires to split removing a translation entry from the v2p list
from actually calling kref_put() for the entry.
Reported-by: Dan Carpenter <[email protected]>
Link: https://lore.kernel.org/lkml/Y+JUIl64UDmdkboh@kadam/
Signed-off-by: Juergen Gross <[email protected]>
---
drivers/xen/xen-scsiback.c | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)
diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index 954188b0b858..294f29cdc7aa 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -1010,12 +1010,6 @@ static int scsiback_add_translation_entry(struct vscsibk_info *info,
return err;
}
-static void __scsiback_del_translation_entry(struct v2p_entry *entry)
-{
- list_del(&entry->l);
- kref_put(&entry->kref, scsiback_free_translation_entry);
-}
-
/*
Delete the translation entry specified
*/
@@ -1024,18 +1018,20 @@ static int scsiback_del_translation_entry(struct vscsibk_info *info,
{
struct v2p_entry *entry;
unsigned long flags;
- int ret = 0;
spin_lock_irqsave(&info->v2p_lock, flags);
/* Find out the translation entry specified */
entry = scsiback_chk_translation_entry(info, v);
if (entry)
- __scsiback_del_translation_entry(entry);
- else
- ret = -ENOENT;
+ list_del(&entry->l);
spin_unlock_irqrestore(&info->v2p_lock, flags);
- return ret;
+
+ if (!entry)
+ return -ENOENT;
+
+ kref_put(&entry->kref, scsiback_free_translation_entry);
+ return 0;
}
static void scsiback_do_add_lun(struct vscsibk_info *info, const char *state,
@@ -1239,14 +1235,19 @@ static void scsiback_release_translation_entry(struct vscsibk_info *info)
{
struct v2p_entry *entry, *tmp;
struct list_head *head = &(info->v2p_entry_lists);
+ struct list_head tmp_list;
unsigned long flags;
spin_lock_irqsave(&info->v2p_lock, flags);
- list_for_each_entry_safe(entry, tmp, head, l)
- __scsiback_del_translation_entry(entry);
+ list_cut_before(&tmp_list, head, head);
spin_unlock_irqrestore(&info->v2p_lock, flags);
+
+ list_for_each_entry_safe(entry, tmp, &tmp_list, l) {
+ list_del(&entry->l);
+ kref_put(&entry->kref, scsiback_free_translation_entry);
+ }
}
static void scsiback_remove(struct xenbus_device *dev)
--
2.35.3
On 28.03.23 11:46, Juergen Gross wrote:
Hello Juergen
> scsiback_free_translation_entry() shouldn't be called under spinlock,
> as it can sleep.
>
> This requires to split removing a translation entry from the v2p list
> from actually calling kref_put() for the entry.
>
> Reported-by: Dan Carpenter <[email protected]>
> Link: https://urldefense.com/v3/__https://lore.kernel.org/lkml/Y*JUIl64UDmdkboh@kadam/__;Kw!!GF_29dbcQIUBPA!23IKdVhamoFq8ptUnprd_TubDMObj-0QAalsGiffBHCeEdOuwrq7z4ohg92Sj0olgl0nh73oXvSr-i1zqXhY$ [lore[.]kernel[.]org]
> Signed-off-by: Juergen Gross <[email protected]>
> ---
> drivers/xen/xen-scsiback.c | 27 ++++++++++++++-------------
> 1 file changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
> index 954188b0b858..294f29cdc7aa 100644
> --- a/drivers/xen/xen-scsiback.c
> +++ b/drivers/xen/xen-scsiback.c
> @@ -1010,12 +1010,6 @@ static int scsiback_add_translation_entry(struct vscsibk_info *info,
> return err;
> }
>
> -static void __scsiback_del_translation_entry(struct v2p_entry *entry)
> -{
> - list_del(&entry->l);
> - kref_put(&entry->kref, scsiback_free_translation_entry);
> -}
> -
> /*
> Delete the translation entry specified
> */
> @@ -1024,18 +1018,20 @@ static int scsiback_del_translation_entry(struct vscsibk_info *info,
> {
> struct v2p_entry *entry;
> unsigned long flags;
> - int ret = 0;
>
> spin_lock_irqsave(&info->v2p_lock, flags);
> /* Find out the translation entry specified */
> entry = scsiback_chk_translation_entry(info, v);
> if (entry)
> - __scsiback_del_translation_entry(entry);
> - else
> - ret = -ENOENT;
> + list_del(&entry->l);
>
> spin_unlock_irqrestore(&info->v2p_lock, flags);
> - return ret;
> +
> + if (!entry)
> + return -ENOENT;
> +
> + kref_put(&entry->kref, scsiback_free_translation_entry);
> + return 0;
> }
>
> static void scsiback_do_add_lun(struct vscsibk_info *info, const char *state,
> @@ -1239,14 +1235,19 @@ static void scsiback_release_translation_entry(struct vscsibk_info *info)
> {
> struct v2p_entry *entry, *tmp;
> struct list_head *head = &(info->v2p_entry_lists);
> + struct list_head tmp_list;
I would use LIST_HEAD(tmp_list);
> unsigned long flags;
>
> spin_lock_irqsave(&info->v2p_lock, flags);
>
> - list_for_each_entry_safe(entry, tmp, head, l)
> - __scsiback_del_translation_entry(entry);
> + list_cut_before(&tmp_list, head, head);
so we just move all entries from head to tmp_list here to be processed...
>
> spin_unlock_irqrestore(&info->v2p_lock, flags);
... when the lock is not held, ok
Patch LGTM, but one (maybe stupid) question to clarify.
Why do we need to use a lock here in the first place? The
scsiback_release_translation_entry() gets called when the driver
instance is about to be removed and *after* the disconnection from
otherend (so no requests are expected), so what else might cause this
list to be accessed concurrently?
> +
> + list_for_each_entry_safe(entry, tmp, &tmp_list, l) {
> + list_del(&entry->l);
> + kref_put(&entry->kref, scsiback_free_translation_entry);
> + }
> }
>
> static void scsiback_remove(struct xenbus_device *dev)
On 28.03.23 17:47, Oleksandr Tyshchenko wrote:
>
>
> On 28.03.23 11:46, Juergen Gross wrote:
>
> Hello Juergen
>
>> scsiback_free_translation_entry() shouldn't be called under spinlock,
>> as it can sleep.
>>
>> This requires to split removing a translation entry from the v2p list
>> from actually calling kref_put() for the entry.
>>
>> Reported-by: Dan Carpenter <[email protected]>
>> Link: https://urldefense.com/v3/__https://lore.kernel.org/lkml/Y*JUIl64UDmdkboh@kadam/__;Kw!!GF_29dbcQIUBPA!23IKdVhamoFq8ptUnprd_TubDMObj-0QAalsGiffBHCeEdOuwrq7z4ohg92Sj0olgl0nh73oXvSr-i1zqXhY$ [lore[.]kernel[.]org]
>> Signed-off-by: Juergen Gross <[email protected]>
>> ---
>> drivers/xen/xen-scsiback.c | 27 ++++++++++++++-------------
>> 1 file changed, 14 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
>> index 954188b0b858..294f29cdc7aa 100644
>> --- a/drivers/xen/xen-scsiback.c
>> +++ b/drivers/xen/xen-scsiback.c
>> @@ -1010,12 +1010,6 @@ static int scsiback_add_translation_entry(struct vscsibk_info *info,
>> return err;
>> }
>>
>> -static void __scsiback_del_translation_entry(struct v2p_entry *entry)
>> -{
>> - list_del(&entry->l);
>> - kref_put(&entry->kref, scsiback_free_translation_entry);
>> -}
>> -
>> /*
>> Delete the translation entry specified
>> */
>> @@ -1024,18 +1018,20 @@ static int scsiback_del_translation_entry(struct vscsibk_info *info,
>> {
>> struct v2p_entry *entry;
>> unsigned long flags;
>> - int ret = 0;
>>
>> spin_lock_irqsave(&info->v2p_lock, flags);
>> /* Find out the translation entry specified */
>> entry = scsiback_chk_translation_entry(info, v);
>> if (entry)
>> - __scsiback_del_translation_entry(entry);
>> - else
>> - ret = -ENOENT;
>> + list_del(&entry->l);
>>
>> spin_unlock_irqrestore(&info->v2p_lock, flags);
>> - return ret;
>> +
>> + if (!entry)
>> + return -ENOENT;
>> +
>> + kref_put(&entry->kref, scsiback_free_translation_entry);
>> + return 0;
>> }
>>
>> static void scsiback_do_add_lun(struct vscsibk_info *info, const char *state,
>> @@ -1239,14 +1235,19 @@ static void scsiback_release_translation_entry(struct vscsibk_info *info)
>> {
>> struct v2p_entry *entry, *tmp;
>> struct list_head *head = &(info->v2p_entry_lists);
>> + struct list_head tmp_list;
>
>
> I would use LIST_HEAD(tmp_list);
There is no need to initialize it, so I think I will keep it as is.
>
>> unsigned long flags;
>>
>> spin_lock_irqsave(&info->v2p_lock, flags);
>>
>> - list_for_each_entry_safe(entry, tmp, head, l)
>> - __scsiback_del_translation_entry(entry);
>> + list_cut_before(&tmp_list, head, head);
>
> so we just move all entries from head to tmp_list here to be processed...
Correct.
>
>>
>> spin_unlock_irqrestore(&info->v2p_lock, flags);
>
> ... when the lock is not held, ok
>
> Patch LGTM, but one (maybe stupid) question to clarify.
>
> Why do we need to use a lock here in the first place? The
> scsiback_release_translation_entry() gets called when the driver
> instance is about to be removed and *after* the disconnection from
> otherend (so no requests are expected), so what else might cause this
> list to be accessed concurrently?
Maybe nothing, but I think it is good practice to keep the lock in order
to avoid future code changes to cause problems.
Juergen
On 29.03.23 09:20, Juergen Gross wrote:
Hello Juergen
> On 28.03.23 17:47, Oleksandr Tyshchenko wrote:
>>
>>
>> On 28.03.23 11:46, Juergen Gross wrote:
>>
>> Hello Juergen
>>
>>> scsiback_free_translation_entry() shouldn't be called under spinlock,
>>> as it can sleep.
>>>
>>> This requires to split removing a translation entry from the v2p list
>>> from actually calling kref_put() for the entry.
>>>
>>> Reported-by: Dan Carpenter <[email protected]>
>>> Link:
>>> https://urldefense.com/v3/__https://lore.kernel.org/lkml/Y*JUIl64UDmdkboh@kadam/__;Kw!!GF_29dbcQIUBPA!23IKdVhamoFq8ptUnprd_TubDMObj-0QAalsGiffBHCeEdOuwrq7z4ohg92Sj0olgl0nh73oXvSr-i1zqXhY$ [lore[.]kernel[.]org]
>>> Signed-off-by: Juergen Gross <[email protected]>
>>> ---
>>> drivers/xen/xen-scsiback.c | 27 ++++++++++++++-------------
>>> 1 file changed, 14 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
>>> index 954188b0b858..294f29cdc7aa 100644
>>> --- a/drivers/xen/xen-scsiback.c
>>> +++ b/drivers/xen/xen-scsiback.c
>>> @@ -1010,12 +1010,6 @@ static int
>>> scsiback_add_translation_entry(struct vscsibk_info *info,
>>> return err;
>>> }
>>> -static void __scsiback_del_translation_entry(struct v2p_entry *entry)
>>> -{
>>> - list_del(&entry->l);
>>> - kref_put(&entry->kref, scsiback_free_translation_entry);
>>> -}
>>> -
>>> /*
>>> Delete the translation entry specified
>>> */
>>> @@ -1024,18 +1018,20 @@ static int
>>> scsiback_del_translation_entry(struct vscsibk_info *info,
>>> {
>>> struct v2p_entry *entry;
>>> unsigned long flags;
>>> - int ret = 0;
>>> spin_lock_irqsave(&info->v2p_lock, flags);
>>> /* Find out the translation entry specified */
>>> entry = scsiback_chk_translation_entry(info, v);
>>> if (entry)
>>> - __scsiback_del_translation_entry(entry);
>>> - else
>>> - ret = -ENOENT;
>>> + list_del(&entry->l);
>>> spin_unlock_irqrestore(&info->v2p_lock, flags);
>>> - return ret;
>>> +
>>> + if (!entry)
>>> + return -ENOENT;
>>> +
>>> + kref_put(&entry->kref, scsiback_free_translation_entry);
>>> + return 0;
>>> }
>>> static void scsiback_do_add_lun(struct vscsibk_info *info, const
>>> char *state,
>>> @@ -1239,14 +1235,19 @@ static void
>>> scsiback_release_translation_entry(struct vscsibk_info *info)
>>> {
>>> struct v2p_entry *entry, *tmp;
>>> struct list_head *head = &(info->v2p_entry_lists);
>>> + struct list_head tmp_list;
>>
>>
>> I would use LIST_HEAD(tmp_list);
>
> There is no need to initialize it, so I think I will keep it as is.
>
>>
>>> unsigned long flags;
>>> spin_lock_irqsave(&info->v2p_lock, flags);
>>> - list_for_each_entry_safe(entry, tmp, head, l)
>>> - __scsiback_del_translation_entry(entry);
>>> + list_cut_before(&tmp_list, head, head);
>>
>> so we just move all entries from head to tmp_list here to be processed...
>
> Correct.
>
>>
>>> spin_unlock_irqrestore(&info->v2p_lock, flags);
>>
>> ... when the lock is not held, ok
>>
>> Patch LGTM, but one (maybe stupid) question to clarify.
>>
>> Why do we need to use a lock here in the first place? The
>> scsiback_release_translation_entry() gets called when the driver
>> instance is about to be removed and *after* the disconnection from
>> otherend (so no requests are expected), so what else might cause this
>> list to be accessed concurrently?
>
> Maybe nothing, but I think it is good practice to keep the lock in order
> to avoid future code changes to cause problems.
Thanks for the explanation, it sounds reasonable to me.
Reviewed-by: Oleksandr Tyshchenko <[email protected]>
>
>
> Juergen
>