Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1293677 > unrolled thread

Re: rhashtable: Prevent spurious EBUSY errors on insertion

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: rhashtable: Prevent spurious EBUSY errors on insertion Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-17 09:50 +0100
    Re: rhashtable: Prevent spurious EBUSY errors on insertion Xin Long <lucien.xin@gmail.com> - 2015-12-17 10:10 +0100
      Re: rhashtable: Prevent spurious EBUSY errors on insertion Xin Long <lucien.xin@gmail.com> - 2015-12-17 17:10 +0100
        Re: rhashtable: Prevent spurious EBUSY errors on insertion Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 03:30 +0100
          Re: rhashtable: Prevent spurious EBUSY errors on insertion Xin Long <lucien.xin@gmail.com> - 2015-12-18 09:20 +0100
      Re: rhashtable: Prevent spurious EBUSY errors on insertion David Miller <davem@davemloft.net> - 2015-12-17 18:10 +0100

#1293677 — Re: rhashtable: Prevent spurious EBUSY errors on insertion

On Thu, Dec 17, 2015 at 04:46:00PM +0800, Xin Long wrote:
>
> sorry for late test, but unfortunately, my case with rhashtalbe still
> return EBUSY.
> I added some debug code in rhashtable_insert_rehash(), and found:
> *future_tbl is null*
> 
> fail:
>         /* Do not fail the insert if someone else did a rehash. */
>         if (likely(rcu_dereference_raw(tbl->future_tbl))) {
>                 printk("future_tbl is there\n");
>                 return 0;
>         } else {
>                 printk("future_tbl is null\n");
>         }
> 
> any idea why ?

That's presumably because you got a genuine double rehash.

Until you post your code we can't really help you.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1293691

On Thu, Dec 17, 2015 at 4:48 PM, Herbert Xu <herbert@gondor.apana.org.au> wrote:
> On Thu, Dec 17, 2015 at 04:46:00PM +0800, Xin Long wrote:
>>
>> sorry for late test, but unfortunately, my case with rhashtalbe still
>> return EBUSY.
>> I added some debug code in rhashtable_insert_rehash(), and found:
>> *future_tbl is null*
>>
>> fail:
>>         /* Do not fail the insert if someone else did a rehash. */
>>         if (likely(rcu_dereference_raw(tbl->future_tbl))) {
>>                 printk("future_tbl is there\n");
>>                 return 0;
>>         } else {
>>                 printk("future_tbl is null\n");
>>         }
>>
>> any idea why ?
>
> That's presumably because you got a genuine double rehash.
>
> Until you post your code we can't really help you.
>
i wish i could , but my codes is a big patch for sctp, and this issue
happens in a special stress test based on this patch.
im trying to think how i can show you. :)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1294013

On Thu, Dec 17, 2015 at 5:00 PM, Xin Long <lucien.xin@gmail.com> wrote:
> On Thu, Dec 17, 2015 at 4:48 PM, Herbert Xu <herbert@gondor.apana.org.au> wrote:
>> On Thu, Dec 17, 2015 at 04:46:00PM +0800, Xin Long wrote:
>>>
>>> sorry for late test, but unfortunately, my case with rhashtalbe still
>>> return EBUSY.
>>> I added some debug code in rhashtable_insert_rehash(), and found:
>>> *future_tbl is null*
>>>
>>> fail:
>>>         /* Do not fail the insert if someone else did a rehash. */
>>>         if (likely(rcu_dereference_raw(tbl->future_tbl))) {
>>>                 printk("future_tbl is there\n");
>>>                 return 0;
>>>         } else {
>>>                 printk("future_tbl is null\n");
>>>         }
>>>
>>> any idea why ?
>>
>> That's presumably because you got a genuine double rehash.
>>
>> Until you post your code we can't really help you.
>>
> i wish i could , but my codes is a big patch for sctp, and this issue
> happens in a special stress test based on this patch.
> im trying to think how i can show you. :)

I'm just wondering, why do not we handle the genuine double rehash
issue inside rhashtable? i mean it's just a temporary error that a
simple retry may fix it.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1294401

On Fri, Dec 18, 2015 at 12:07:08AM +0800, Xin Long wrote:
>
> I'm just wondering, why do not we handle the genuine double rehash
> issue inside rhashtable? i mean it's just a temporary error that a
> simple retry may fix it.

Because a double rehash means that someone has cracked your hash
function and there is no point in trying anymore.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1294491

On Fri, Dec 18, 2015 at 10:26 AM, Herbert Xu
<herbert@gondor.apana.org.au> wrote:
> On Fri, Dec 18, 2015 at 12:07:08AM +0800, Xin Long wrote:
>>
>> I'm just wondering, why do not we handle the genuine double rehash
>> issue inside rhashtable? i mean it's just a temporary error that a
>> simple retry may fix it.
>
> Because a double rehash means that someone has cracked your hash
> function and there is no point in trying anymore.

ok, get your point, is it possible to be triggered by some cases under
a big stress insertion, but they are all legal cases. like we use rhash in
nftables, if there are a big batch sets to insert, may this issue happen?

>
> Cheers,
> --
> Email: Herbert Xu <herbert@gondor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1294052

From: Xin Long <lucien.xin@gmail.com>
Date: Thu, 17 Dec 2015 17:00:35 +0800

> On Thu, Dec 17, 2015 at 4:48 PM, Herbert Xu <herbert@gondor.apana.org.au> wrote:
>> On Thu, Dec 17, 2015 at 04:46:00PM +0800, Xin Long wrote:
>>>
>>> sorry for late test, but unfortunately, my case with rhashtalbe still
>>> return EBUSY.
>>> I added some debug code in rhashtable_insert_rehash(), and found:
>>> *future_tbl is null*
>>>
>>> fail:
>>>         /* Do not fail the insert if someone else did a rehash. */
>>>         if (likely(rcu_dereference_raw(tbl->future_tbl))) {
>>>                 printk("future_tbl is there\n");
>>>                 return 0;
>>>         } else {
>>>                 printk("future_tbl is null\n");
>>>         }
>>>
>>> any idea why ?
>>
>> That's presumably because you got a genuine double rehash.
>>
>> Until you post your code we can't really help you.
>>
> i wish i could , but my codes is a big patch for sctp, and this issue
> happens in a special stress test based on this patch.
> im trying to think how i can show you. :)

Simply post it.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web