Re: Crashes/hung tasks with z3pool under memory pressure

Re: Crashes/hung tasks with z3pool under memory pressure

[Vitaly Wool]

Hi Guenter,

> [ ... ]
> > Ugh. Could you please keep that patch and apply this on top:
> > 
> > diff --git a/mm/z3fold.c b/mm/z3fold.c
> > index c0bca6153b95..e8a80d044d9e 100644
> > --- a/mm/z3fold.c
> > +++ b/mm/z3fold.c
> > @@ -840,6 +840,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> >                       kref_get(&zhdr->refcount);
> >                       list_del_init(&zhdr->buddy);
> >                       zhdr->cpu = -1;
> > +                     break;
> >               }
> >               list_del_init(&page->lru);
> > 
> Much better, in a way. The system now takes much longer to crash,
> and the crash reason is a bit different. The log is too long to attach,
> so I copied it to [1].
> 
> crashdump.0002                  Latest log
> 000[12]-Fix-attempt-[12].patch  Patches applied on top of v4.17.0-rc1.

thanks for the update. Let's start from a clean sheet. I believe this patch has to be applied anyway so could you please check if it solves the problem. 

diff --git a/mm/z3fold.c b/mm/z3fold.c
index c0bca6153b95..059fb3d5ca86 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -144,7 +144,8 @@ enum z3fold_page_flags {
 	PAGE_HEADLESS = 0,
 	MIDDLE_CHUNK_MAPPED,
 	NEEDS_COMPACTING,
-	PAGE_STALE
+	PAGE_STALE,
+	UNDER_RECLAIM
 };
 
 /*****************
@@ -173,6 +174,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
 	clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 	clear_bit(NEEDS_COMPACTING, &page->private);
 	clear_bit(PAGE_STALE, &page->private);
+	clear_bit(UNDER_RECLAIM, &page->private);
 
 	spin_lock_init(&zhdr->page_lock);
 	kref_init(&zhdr->refcount);
@@ -756,6 +758,10 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 		atomic64_dec(&pool->pages_nr);
 		return;
 	}
+	if (test_bit(UNDER_RECLAIM, &page->private)) {
+		z3fold_page_unlock(zhdr);
+		return;
+	}
 	if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
 		z3fold_page_unlock(zhdr);
 		return;
@@ -840,6 +846,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 			kref_get(&zhdr->refcount);
 			list_del_init(&zhdr->buddy);
 			zhdr->cpu = -1;
+			set_bit(UNDER_RECLAIM, &page->private);
+			break;
 		}
 
 		list_del_init(&page->lru);
@@ -888,6 +896,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 		}
 next:
 		spin_lock(&pool->lock);
+		clear_bit(UNDER_RECLAIM, &page->private);
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
 			if (ret == 0) {
 				spin_unlock(&pool->lock);

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

On Tue, Apr 17, 2018 at 04:00:32PM +0200, Vitaly Wool wrote:
> Hi Guenter,
> 
> > [ ... ]
> > > Ugh. Could you please keep that patch and apply this on top:
> > > 
> > > diff --git a/mm/z3fold.c b/mm/z3fold.c
> > > index c0bca6153b95..e8a80d044d9e 100644
> > > --- a/mm/z3fold.c
> > > +++ b/mm/z3fold.c
> > > @@ -840,6 +840,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> > >                       kref_get(&zhdr->refcount);
> > >                       list_del_init(&zhdr->buddy);
> > >                       zhdr->cpu = -1;
> > > +                     break;
> > >               }
> > >               list_del_init(&page->lru);
> > > 
> > Much better, in a way. The system now takes much longer to crash,
> > and the crash reason is a bit different. The log is too long to attach,
> > so I copied it to [1].
> > 
> > crashdump.0002                  Latest log
> > 000[12]-Fix-attempt-[12].patch  Patches applied on top of v4.17.0-rc1.
> 
> thanks for the update. Let's start from a clean sheet. I believe this patch has to be applied anyway so could you please check if it solves the problem. 
> 

Getting better; the log is much less noisy. Unfortunately, there are still
locking problems, resulting in a hung task. I copied the log message to [1].
This is with [2] applied on top of v4.17-rc1.

Guenter

---
[1] http://server.roeck-us.net/qemu/z3pool/crashdump.0003
[2] http://server.roeck-us.net/qemu/z3pool/0001-Fix-attempt-3.patch

Re: Crashes/hung tasks with z3pool under memory pressure

[Vitaly Wool]

Den tis 17 apr. 2018 kl 18:35 skrev Guenter Roeck <linux@roeck-us.net>:

<snip>

> Getting better; the log is much less noisy. Unfortunately, there are still
> locking problems, resulting in a hung task. I copied the log message to [1].
> This is with [2] applied on top of v4.17-rc1.

Now this version (this is a full patch to be applied instead of the previous one) should have the above problem resolved too:

diff --git a/mm/z3fold.c b/mm/z3fold.c
index c0bca6153b95..901c0b07cbda 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -144,7 +144,8 @@ enum z3fold_page_flags {
 	PAGE_HEADLESS = 0,
 	MIDDLE_CHUNK_MAPPED,
 	NEEDS_COMPACTING,
-	PAGE_STALE
+	PAGE_STALE,
+	UNDER_RECLAIM
 };
 
 /*****************
@@ -173,6 +174,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
 	clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
 	clear_bit(NEEDS_COMPACTING, &page->private);
 	clear_bit(PAGE_STALE, &page->private);
+	clear_bit(UNDER_RECLAIM, &page->private);
 
 	spin_lock_init(&zhdr->page_lock);
 	kref_init(&zhdr->refcount);
@@ -756,6 +758,10 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 		atomic64_dec(&pool->pages_nr);
 		return;
 	}
+	if (test_bit(UNDER_RECLAIM, &page->private)) {
+		z3fold_page_unlock(zhdr);
+		return;
+	}
 	if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
 		z3fold_page_unlock(zhdr);
 		return;
@@ -840,6 +846,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 			kref_get(&zhdr->refcount);
 			list_del_init(&zhdr->buddy);
 			zhdr->cpu = -1;
+			set_bit(UNDER_RECLAIM, &page->private);
+			break;
 		}
 
 		list_del_init(&page->lru);
@@ -887,25 +895,35 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 				goto next;
 		}
 next:
-		spin_lock(&pool->lock);
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
 			if (ret == 0) {
-				spin_unlock(&pool->lock);
 				free_z3fold_page(page);
 				return 0;
 			}
-		} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
-			atomic64_dec(&pool->pages_nr);
+			spin_lock(&pool->lock);
+			list_add(&page->lru, &pool->lru);
+			spin_unlock(&pool->lock);
+		} else {
+			z3fold_page_lock(zhdr);
+			clear_bit(UNDER_RECLAIM, &page->private);
+			 if (kref_put(&zhdr->refcount,
+					release_z3fold_page_locked)) {
+				atomic64_dec(&pool->pages_nr);
+				return 0;
+			}
+			/*
+			 * if we are here, the page is still not completely
+			 * free. Take the global pool lock then to be able
+			 * to add it back to the lru list
+			 */
+			spin_lock(&pool->lock);
+			list_add(&page->lru, &pool->lru);
 			spin_unlock(&pool->lock);
-			return 0;
+			z3fold_page_unlock(zhdr);
 		}
 
-		/*
-		 * Add to the beginning of LRU.
-		 * Pool lock has to be kept here to ensure the page has
-		 * not already been released
-		 */
-		list_add(&page->lru, &pool->lru);
+		/* We started off locked to we need to lock the pool back */
+		spin_lock(&pool->lock);
 	}
 	spin_unlock(&pool->lock);
 	return -EAGAIN;

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

On Wed, Apr 18, 2018 at 10:13:17AM +0200, Vitaly Wool wrote:
> Den tis 17 apr. 2018 kl 18:35 skrev Guenter Roeck <linux@roeck-us.net>:
> 
> <snip>
> 
> > Getting better; the log is much less noisy. Unfortunately, there are still
> > locking problems, resulting in a hung task. I copied the log message to [1].
> > This is with [2] applied on top of v4.17-rc1.
> 
> Now this version (this is a full patch to be applied instead of the previous one) should have the above problem resolved too:
> 

Excellent - I can not reproduce the problem with this patch
applied.

Guenter

> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index c0bca6153b95..901c0b07cbda 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -144,7 +144,8 @@ enum z3fold_page_flags {
>  	PAGE_HEADLESS = 0,
>  	MIDDLE_CHUNK_MAPPED,
>  	NEEDS_COMPACTING,
> -	PAGE_STALE
> +	PAGE_STALE,
> +	UNDER_RECLAIM
>  };
>  
>  /*****************
> @@ -173,6 +174,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
>  	clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
>  	clear_bit(NEEDS_COMPACTING, &page->private);
>  	clear_bit(PAGE_STALE, &page->private);
> +	clear_bit(UNDER_RECLAIM, &page->private);
>  
>  	spin_lock_init(&zhdr->page_lock);
>  	kref_init(&zhdr->refcount);
> @@ -756,6 +758,10 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>  		atomic64_dec(&pool->pages_nr);
>  		return;
>  	}
> +	if (test_bit(UNDER_RECLAIM, &page->private)) {
> +		z3fold_page_unlock(zhdr);
> +		return;
> +	}
>  	if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
>  		z3fold_page_unlock(zhdr);
>  		return;
> @@ -840,6 +846,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>  			kref_get(&zhdr->refcount);
>  			list_del_init(&zhdr->buddy);
>  			zhdr->cpu = -1;
> +			set_bit(UNDER_RECLAIM, &page->private);
> +			break;
>  		}
>  
>  		list_del_init(&page->lru);
> @@ -887,25 +895,35 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>  				goto next;
>  		}
>  next:
> -		spin_lock(&pool->lock);
>  		if (test_bit(PAGE_HEADLESS, &page->private)) {
>  			if (ret == 0) {
> -				spin_unlock(&pool->lock);
>  				free_z3fold_page(page);
>  				return 0;
>  			}
> -		} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
> -			atomic64_dec(&pool->pages_nr);
> +			spin_lock(&pool->lock);
> +			list_add(&page->lru, &pool->lru);
> +			spin_unlock(&pool->lock);
> +		} else {
> +			z3fold_page_lock(zhdr);
> +			clear_bit(UNDER_RECLAIM, &page->private);
> +			 if (kref_put(&zhdr->refcount,
> +					release_z3fold_page_locked)) {
> +				atomic64_dec(&pool->pages_nr);
> +				return 0;
> +			}
> +			/*
> +			 * if we are here, the page is still not completely
> +			 * free. Take the global pool lock then to be able

extra then ?

> +			 * to add it back to the lru list
> +			 */
> +			spin_lock(&pool->lock);
> +			list_add(&page->lru, &pool->lru);
>  			spin_unlock(&pool->lock);
> -			return 0;
> +			z3fold_page_unlock(zhdr);
>  		}
>  
> -		/*
> -		 * Add to the beginning of LRU.
> -		 * Pool lock has to be kept here to ensure the page has
> -		 * not already been released
> -		 */
> -		list_add(&page->lru, &pool->lru);
> +		/* We started off locked to we need to lock the pool back */
> +		spin_lock(&pool->lock);
>  	}
>  	spin_unlock(&pool->lock);
>  	return -EAGAIN;

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

Hi Vitaly,

On Thu, Apr 19, 2018 at 08:18:51AM +0000, Vitaly Wool wrote:
> Hi Guenter,
> 
> Den ons 18 apr. 2018 kl 18:07 skrev Guenter Roeck <linux@roeck-us.net>:
> 
> > On Wed, Apr 18, 2018 at 10:13:17AM +0200, Vitaly Wool wrote:
> > > Den tis 17 apr. 2018 kl 18:35 skrev Guenter Roeck <linux@roeck-us.net>:
> > >
> > > <snip>
> > >
> > > > Getting better; the log is much less noisy. Unfortunately, there are
> > still
> > > > locking problems, resulting in a hung task. I copied the log message
> > to [1].
> > > > This is with [2] applied on top of v4.17-rc1.
> > >
> > > Now this version (this is a full patch to be applied instead of the
> > previous one) should have the above problem resolved too:
> > >
> >
> > Excellent - I can not reproduce the problem with this patch
> > applied.
> >
> > thank you very much for testing and prompt feedback. I'll come up shortly
> with the final patch.
> 

Any updates ?

Thanks,
Guenter

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

On Tue, Apr 17, 2018 at 12:14:37AM +0200, Vitaly Wool wrote:
[ ... ]
> Ugh. Could you please keep that patch and apply this on top:
> 
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index c0bca6153b95..e8a80d044d9e 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -840,6 +840,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>  			kref_get(&zhdr->refcount);
>  			list_del_init(&zhdr->buddy);
>  			zhdr->cpu = -1;
> +			break;
>  		}
>  		list_del_init(&page->lru);
> 
Much better, in a way. The system now takes much longer to crash,
and the crash reason is a bit different. The log is too long to attach,
so I copied it to [1].

crashdump.0002			Latest log
000[12]-Fix-attempt-[12].patch	Patches applied on top of v4.17.0-rc1.

Hope it helps,
Guenter


[1] http://server.roeck-us.net/qemu/z3pool/

Re: Crashes/hung tasks with z3pool under memory pressure

[Vitaly Wool]

On 4/16/18 5:58 PM, Guenter Roeck wrote:

> On Mon, Apr 16, 2018 at 02:43:01PM +0200, Vitaly Wool wrote:
>> Hey Guenter,
>>
>> On 04/13/2018 07:56 PM, Guenter Roeck wrote:
>>
>>> On Fri, Apr 13, 2018 at 05:40:18PM +0000, Vitaly Wool wrote:
>>>> On Fri, Apr 13, 2018, 7:35 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>>>
>>>>> On Fri, Apr 13, 2018 at 05:21:02AM +0000, Vitaly Wool wrote:
>>>>>> Hi Guenter,
>>>>>>
>>>>>>
>>>>>> Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <linux@roeck-us.net>:
>>>>>>
>>>>>>> Hi all,
>>>>>>> we are observing crashes with z3pool under memory pressure. The kernel
>>>>>> version
>>>>>>> used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
>>>>>> problem was
>>>>>>> also seen with v4.14 based kernels.
>>>>>> just before I dig into this, could you please try reproducing the errors
>>>>>> you see with https://patchwork.kernel.org/patch/10210459/ applied?
>>>>>>
>>>>> As mentioned above, I tested with v4.16-11827-g5d1365940a68, which already
>>>>> includes this patch.
>>>>>
>>>> Bah. Sorry. Expect an update after the weekend.
>>>>
>>> NP; easy to miss. Thanks a lot for looking into it.
>>>
>> I wonder if the following patch would make a difference:
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index c0bca6153b95..5e547c2d5832 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -887,19 +887,21 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>>   				goto next;
>>   		}
>>   next:
>> -		spin_lock(&pool->lock);
>>   		if (test_bit(PAGE_HEADLESS, &page->private)) {
>>   			if (ret == 0) {
>> -				spin_unlock(&pool->lock);
>>   				free_z3fold_page(page);
>>   				return 0;
>>   			}
>> -		} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
>> -			atomic64_dec(&pool->pages_nr);
>> -			spin_unlock(&pool->lock);
>> -			return 0;
>> +		} else {
>> +			spin_lock(&zhdr->page_lock);
>> +			if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
>> +				atomic64_dec(&pool->pages_nr);
>> +				return 0;
>> +			}
>> +			spin_unlock(&zhdr->page_lock);
>>   		}
>> +		spin_lock(&pool->lock);
>>   		/*
>>   		 * Add to the beginning of LRU.
>>   		 * Pool lock has to be kept here to ensure the page has
>>
> No, it doesn't. Same crash.
>
> BUG: MAX_LOCK_DEPTH too low!
> turning off the locking correctness validator.
> depth: 48  max: 48!
> 48 locks held by kswapd0/51:
>   #0: 000000004d7a35a9 (&(&pool->lock)->rlock#3){+.+.}, at: z3fold_zpool_shrink+0x47/0x3e0
>   #1: 000000007739f49e (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
>   #2: 00000000ff6cd4c8 (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
>   #3: 000000004cffc6cb (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
> ...
> PU: 0 PID: 51 Comm: kswapd0 Not tainted 4.17.0-rc1-yocto-standard+ #11
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1 04/01/2014
> Call Trace:
>   dump_stack+0x67/0x9b
>   __lock_acquire+0x429/0x18f0
>   ? __lock_acquire+0x2af/0x18f0
>   ? __lock_acquire+0x2af/0x18f0
>   ? lock_acquire+0x93/0x230
>   lock_acquire+0x93/0x230
>   ? z3fold_zpool_shrink+0xb7/0x3e0
>   _raw_spin_trylock+0x65/0x80
>   ? z3fold_zpool_shrink+0xb7/0x3e0
>   ? z3fold_zpool_shrink+0x47/0x3e0
>   z3fold_zpool_shrink+0xb7/0x3e0
>   zswap_frontswap_store+0x180/0x7c0
> ...
> BUG: sleeping function called from invalid context at mm/page_alloc.c:4320
> in_atomic(): 1, irqs_disabled(): 0, pid: 51, name: kswapd0
> INFO: lockdep is turned off.
> Preemption disabled at:
> [<0000000000000000>]           (null)
> CPU: 0 PID: 51 Comm: kswapd0 Not tainted 4.17.0-rc1-yocto-standard+ #11
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1 04/01/2014
> Call Trace:
>   dump_stack+0x67/0x9b
>   ___might_sleep+0x16c/0x250
>   __alloc_pages_nodemask+0x1e7/0x1490
>   ? lock_acquire+0x93/0x230
>   ? lock_acquire+0x93/0x230
>   __read_swap_cache_async+0x14d/0x260
>   zswap_writeback_entry+0xdb/0x340
>   z3fold_zpool_shrink+0x2b1/0x3e0
>   zswap_frontswap_store+0x180/0x7c0
>   ? page_vma_mapped_walk+0x22/0x230
>   __frontswap_store+0x6e/0xf0
>   swap_writepage+0x49/0x70
> ...
>
> This is with your patch applied on top of v4.17-rc1.
>
> Guenter
>
Ugh. Could you please keep that patch and apply this on top:

diff --git a/mm/z3fold.c b/mm/z3fold.c
index c0bca6153b95..e8a80d044d9e 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -840,6 +840,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
  			kref_get(&zhdr->refcount);
  			list_del_init(&zhdr->buddy);
  			zhdr->cpu = -1;
+			break;
  		}
  
  		list_del_init(&page->lru);

Thanks,
    Vitaly

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

On Mon, Apr 16, 2018 at 02:43:01PM +0200, Vitaly Wool wrote:
> Hey Guenter,
> 
> On 04/13/2018 07:56 PM, Guenter Roeck wrote:
> 
> >On Fri, Apr 13, 2018 at 05:40:18PM +0000, Vitaly Wool wrote:
> >>On Fri, Apr 13, 2018, 7:35 PM Guenter Roeck <linux@roeck-us.net> wrote:
> >>
> >>>On Fri, Apr 13, 2018 at 05:21:02AM +0000, Vitaly Wool wrote:
> >>>>Hi Guenter,
> >>>>
> >>>>
> >>>>Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <linux@roeck-us.net>:
> >>>>
> >>>>>Hi all,
> >>>>>we are observing crashes with z3pool under memory pressure. The kernel
> >>>>version
> >>>>>used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
> >>>>problem was
> >>>>>also seen with v4.14 based kernels.
> >>>>
> >>>>just before I dig into this, could you please try reproducing the errors
> >>>>you see with https://patchwork.kernel.org/patch/10210459/ applied?
> >>>>
> >>>As mentioned above, I tested with v4.16-11827-g5d1365940a68, which already
> >>>includes this patch.
> >>>
> >>Bah. Sorry. Expect an update after the weekend.
> >>
> >NP; easy to miss. Thanks a lot for looking into it.
> >
> I wonder if the following patch would make a difference:
> 
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index c0bca6153b95..5e547c2d5832 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -887,19 +887,21 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>  				goto next;
>  		}
>  next:
> -		spin_lock(&pool->lock);
>  		if (test_bit(PAGE_HEADLESS, &page->private)) {
>  			if (ret == 0) {
> -				spin_unlock(&pool->lock);
>  				free_z3fold_page(page);
>  				return 0;
>  			}
> -		} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
> -			atomic64_dec(&pool->pages_nr);
> -			spin_unlock(&pool->lock);
> -			return 0;
> +		} else {
> +			spin_lock(&zhdr->page_lock);
> +			if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
> +				atomic64_dec(&pool->pages_nr);
> +				return 0;
> +			}
> +			spin_unlock(&zhdr->page_lock);
>  		}
> +		spin_lock(&pool->lock);
>  		/*
>  		 * Add to the beginning of LRU.
>  		 * Pool lock has to be kept here to ensure the page has
> 
No, it doesn't. Same crash.

BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48  max: 48!
48 locks held by kswapd0/51:
 #0: 000000004d7a35a9 (&(&pool->lock)->rlock#3){+.+.}, at: z3fold_zpool_shrink+0x47/0x3e0
 #1: 000000007739f49e (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
 #2: 00000000ff6cd4c8 (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
 #3: 000000004cffc6cb (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
...
PU: 0 PID: 51 Comm: kswapd0 Not tainted 4.17.0-rc1-yocto-standard+ #11
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1 04/01/2014
Call Trace:
 dump_stack+0x67/0x9b
 __lock_acquire+0x429/0x18f0
 ? __lock_acquire+0x2af/0x18f0
 ? __lock_acquire+0x2af/0x18f0
 ? lock_acquire+0x93/0x230
 lock_acquire+0x93/0x230
 ? z3fold_zpool_shrink+0xb7/0x3e0
 _raw_spin_trylock+0x65/0x80
 ? z3fold_zpool_shrink+0xb7/0x3e0
 ? z3fold_zpool_shrink+0x47/0x3e0
 z3fold_zpool_shrink+0xb7/0x3e0
 zswap_frontswap_store+0x180/0x7c0
...
BUG: sleeping function called from invalid context at mm/page_alloc.c:4320
in_atomic(): 1, irqs_disabled(): 0, pid: 51, name: kswapd0
INFO: lockdep is turned off.
Preemption disabled at:
[<0000000000000000>]           (null)
CPU: 0 PID: 51 Comm: kswapd0 Not tainted 4.17.0-rc1-yocto-standard+ #11
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1 04/01/2014
Call Trace:
 dump_stack+0x67/0x9b
 ___might_sleep+0x16c/0x250
 __alloc_pages_nodemask+0x1e7/0x1490
 ? lock_acquire+0x93/0x230
 ? lock_acquire+0x93/0x230
 __read_swap_cache_async+0x14d/0x260
 zswap_writeback_entry+0xdb/0x340
 z3fold_zpool_shrink+0x2b1/0x3e0
 zswap_frontswap_store+0x180/0x7c0
 ? page_vma_mapped_walk+0x22/0x230
 __frontswap_store+0x6e/0xf0
 swap_writepage+0x49/0x70
...

This is with your patch applied on top of v4.17-rc1.

Guenter

Re: Crashes/hung tasks with z3pool under memory pressure

[Vitaly Wool]

Hey Guenter,

On 04/13/2018 07:56 PM, Guenter Roeck wrote:

> On Fri, Apr 13, 2018 at 05:40:18PM +0000, Vitaly Wool wrote:
>> On Fri, Apr 13, 2018, 7:35 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>>> On Fri, Apr 13, 2018 at 05:21:02AM +0000, Vitaly Wool wrote:
>>>> Hi Guenter,
>>>>
>>>>
>>>> Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <linux@roeck-us.net>:
>>>>
>>>>> Hi all,
>>>>> we are observing crashes with z3pool under memory pressure. The kernel
>>>> version
>>>>> used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
>>>> problem was
>>>>> also seen with v4.14 based kernels.
>>>>
>>>> just before I dig into this, could you please try reproducing the errors
>>>> you see with https://patchwork.kernel.org/patch/10210459/ applied?
>>>>
>>> As mentioned above, I tested with v4.16-11827-g5d1365940a68, which already
>>> includes this patch.
>>>
>> Bah. Sorry. Expect an update after the weekend.
>>
> NP; easy to miss. Thanks a lot for looking into it.
>
I wonder if the following patch would make a difference:

diff --git a/mm/z3fold.c b/mm/z3fold.c
index c0bca6153b95..5e547c2d5832 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -887,19 +887,21 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
  				goto next;
  		}
  next:
-		spin_lock(&pool->lock);
  		if (test_bit(PAGE_HEADLESS, &page->private)) {
  			if (ret == 0) {
-				spin_unlock(&pool->lock);
  				free_z3fold_page(page);
  				return 0;
  			}
-		} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
-			atomic64_dec(&pool->pages_nr);
-			spin_unlock(&pool->lock);
-			return 0;
+		} else {
+			spin_lock(&zhdr->page_lock);
+			if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
+				atomic64_dec(&pool->pages_nr);
+				return 0;
+			}
+			spin_unlock(&zhdr->page_lock);
  		}
  
+		spin_lock(&pool->lock);
  		/*
  		 * Add to the beginning of LRU.
  		 * Pool lock has to be kept here to ensure the page has


Thanks,
    Vitaly

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

On Fri, Apr 13, 2018 at 05:40:18PM +0000, Vitaly Wool wrote:
> On Fri, Apr 13, 2018, 7:35 PM Guenter Roeck <linux@roeck-us.net> wrote:
> 
> > On Fri, Apr 13, 2018 at 05:21:02AM +0000, Vitaly Wool wrote:
> > > Hi Guenter,
> > >
> > >
> > > Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <linux@roeck-us.net>:
> > >
> > > > Hi all,
> > >
> > > > we are observing crashes with z3pool under memory pressure. The kernel
> > > version
> > > > used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
> > > problem was
> > > > also seen with v4.14 based kernels.
> > >
> > >
> > > just before I dig into this, could you please try reproducing the errors
> > > you see with https://patchwork.kernel.org/patch/10210459/ applied?
> > >
> >
> > As mentioned above, I tested with v4.16-11827-g5d1365940a68, which already
> > includes this patch.
> >
> 
> Bah. Sorry. Expect an update after the weekend.
> 
NP; easy to miss. Thanks a lot for looking into it.

Guenter

Re: Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

On Fri, Apr 13, 2018 at 05:21:02AM +0000, Vitaly Wool wrote:
> Hi Guenter,
> 
> 
> Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <linux@roeck-us.net>:
> 
> > Hi all,
> 
> > we are observing crashes with z3pool under memory pressure. The kernel
> version
> > used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
> problem was
> > also seen with v4.14 based kernels.
> 
> 
> just before I dig into this, could you please try reproducing the errors
> you see with https://patchwork.kernel.org/patch/10210459/ applied?
> 

As mentioned above, I tested with v4.16-11827-g5d1365940a68, which already
includes this patch.

$ git log --oneline v4.14..5d1365940a68 mm/z3fold.c
8a97ea546bb6 mm/z3fold.c: use gfpflags_allow_blocking
1ec6995d1290 z3fold: fix memory leak
5c9bab592f53 z3fold: limit use of stale list for allocation
f144c390f905 mm: docs: fix parameter names mismatch
5d03a6613957 mm/z3fold.c: use kref to prevent page free/compact race

Guenter

Re: Crashes/hung tasks with z3pool under memory pressure

[Vitaly Wool]

Hi Guenter,


Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <linux@roeck-us.net>:

> Hi all,

> we are observing crashes with z3pool under memory pressure. The kernel
version
> used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
problem was
> also seen with v4.14 based kernels.


just before I dig into this, could you please try reproducing the errors
you see with https://patchwork.kernel.org/patch/10210459/ applied?

Thanks,
    Vitaly

> For simplicity, here is a set of shortened logs. A more complete log is
> available at [1].

> ------------[ cut here ]------------
> DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >= PREEMPT_MASK - 10)
> WARNING: CPU: 2 PID: 594 at kernel/sched/core.c:3212
preempt_count_add+0x90/0xa0
> Modules linked in:
> CPU: 2 PID: 594 Comm: memory-eater Not tainted 4.16.0-yocto-standard+ #8
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1
04/01/2014
> RIP: 0010:preempt_count_add+0x90/0xa0
> RSP: 0000:ffffb12740db7750 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 00000000000000f6
> RDX: 00000000000000f6 RSI: 0000000000000082 RDI: 00000000ffffffff
> RBP: fffff00480f357a0 R08: 000000000000004a R09: 00000000000001ad
> R10: ffffb12740db77e0 R11: 0000000000000000 R12: ffff9cbc7e265d10
> R13: ffff9cbc7cd5e000 R14: ffff9cbc7a7000d8 R15: fffff00480f35780
> FS:  00007f5140791700(0000) GS:ffff9cbc7fd00000(0000)
knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f513260f000 CR3: 0000000032086000 CR4: 00000000000006e0
> Call Trace:
>   _raw_spin_trylock+0x13/0x30
>   z3fold_zpool_shrink+0xab/0x3a0
>   zswap_frontswap_store+0x10b/0x610
> ...
> WARNING: CPU: 1 PID: 92 at mm/z3fold.c:278
release_z3fold_page_locked+0x25/0x40
> Modules linked in:
> ...
> INFO: rcu_preempt self-detected stall on CPU
>          2-...!: (20958 ticks this GP) idle=5da/1/4611686018427387906
>          softirq=4104/4113 fqs=11
> ...
> RIP: 0010:queued_spin_lock_slowpath+0x132/0x190
> RSP: 0000:ffffb12740db7750 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
> RAX: 0000000000100101 RBX: ffff9cbc7a7000c8 RCX: 0000000000000001
> RDX: 0000000000000101 RSI: 0000000000000001 RDI: 0000000000000101
> RBP: 0000000000000000 R08: ffff9cbc7fc21240 R09: ffffffffaf19c900
> R10: ffffb12740db75a0 R11: 0000000000000010 R12: fffff00480522d20
> R13: ffff9cbc548b4000 R14: ffff9cbc7a7000d8 R15: fffff00480522d00
>   ? __zswap_pool_current+0x80/0x90
>   z3fold_zpool_shrink+0x1d3/0x3a0
>   zswap_frontswap_store+0x10b/0x610
> ...

> With lock debugging enabled, the log is a bit different, but similar.

> BUG: MAX_LOCK_DEPTH too low!
> turning off the locking correctness validator.
> depth: 48  max: 48!
> 48 locks held by memory-eater/619:
>   #0: 000000002da807ce (&mm->mmap_sem){++++}, at:
__do_page_fault+0x122/0x5a0
>   #1: 0000000012fa6629 (&(&pool->lock)->rlock#3){+.+.}, at:
z3fold_zpool_shrink+0x47/0x3e0
>   #2: 00000000c85f45dd (&(&zhdr->page_lock)->rlock){+.+.}, at:
z3fold_zpool_shrink+0xb7/0x3e0
>   #3: 00000000876f5fdc (&(&zhdr->page_lock)->rlock){+.+.}, at:
z3fold_zpool_shrink+0xb7/0x3e0
> ...
> watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [memory-eater:613]
> Modules linked in:
> irq event stamp: 1435394
> hardirqs last  enabled at (1435393): [<ffffffff9b90ed81>]
> _raw_spin_unlock_irqrestore+0x51/0x60
> hardirqs last disabled at (1435394): [<ffffffff9b907baa>]
__schedule+0xba/0xbb0
> softirqs last  enabled at (1434508): [<ffffffff9bc0027c>]
__do_softirq+0x27c/0x516
> softirqs last disabled at (1434323): [<ffffffff9b069a29>]
irq_exit+0xa9/0xc0
> CPU: 0 PID: 613 Comm: memory-eater Tainted: G        W
> 4.16.0-yocto-standard+ #9
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1
04/01/2014
> RIP: 0010:queued_spin_lock_slowpath+0x177/0x1a0
> RSP: 0000:ffffa61f80e074e0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
> RAX: 0000000000000000 RBX: ffff9704379cba08 RCX: ffff97043fc22080
> RDX: 0000000000000001 RSI: ffffffff9c05f6a0 RDI: 0000000000040000
> RBP: 0000000000000000 R08: ffffffff9b1f2215 R09: 0000000000000000
> R10: ffffa61f80e07490 R11: ffff9704379cba20 R12: ffff97043fc22080
> R13: ffffde77404e0920 R14: ffff970413824000 R15: ffff9704379cba00
> FS:  00007f8c6317f700(0000) GS:ffff97043fc00000(0000)
knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f8c43f3d010 CR3: 000000003aba0000 CR4: 00000000000006f0
> Call Trace:
>   do_raw_spin_lock+0xad/0xb0
>   z3fold_zpool_malloc+0x595/0x790
> ...

> The problem is easy to reproduce. Please see [2] and the other files
> at [3] for details. Various additional crash logs, observed with
> chromeos-4.14, are available at [4].

> Please let me know if there is anything else I can do to help solving
> or debugging the problem. I had a look into the code, but I must admit
> that its locking is a mystery to me.

> Thanks,
> Guenter

> ---
> [1] http://server.roeck-us.net/qemu/z3pool/crashdump
> [2] http://server.roeck-us.net/qemu/z3pool/README
> [3] http://server.roeck-us.net/qemu/z3pool/
> [4] https://bugs.chromium.org/p/chromium/issues/detail?id=822360

Crashes/hung tasks with z3pool under memory pressure

[Guenter Roeck]

Hi all,

we are observing crashes with z3pool under memory pressure. The kernel version
used to reproduce the problem is v4.16-11827-g5d1365940a68, but the problem was
also seen with v4.14 based kernels.

For simplicity, here is a set of shortened logs. A more complete log is
available at [1].

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >= PREEMPT_MASK - 10)
WARNING: CPU: 2 PID: 594 at kernel/sched/core.c:3212 preempt_count_add+0x90/0xa0
Modules linked in:
CPU: 2 PID: 594 Comm: memory-eater Not tainted 4.16.0-yocto-standard+ #8
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1 04/01/2014
RIP: 0010:preempt_count_add+0x90/0xa0
RSP: 0000:ffffb12740db7750 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 00000000000000f6
RDX: 00000000000000f6 RSI: 0000000000000082 RDI: 00000000ffffffff
RBP: fffff00480f357a0 R08: 000000000000004a R09: 00000000000001ad
R10: ffffb12740db77e0 R11: 0000000000000000 R12: ffff9cbc7e265d10
R13: ffff9cbc7cd5e000 R14: ffff9cbc7a7000d8 R15: fffff00480f35780
FS:  00007f5140791700(0000) GS:ffff9cbc7fd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f513260f000 CR3: 0000000032086000 CR4: 00000000000006e0
Call Trace:
 _raw_spin_trylock+0x13/0x30
 z3fold_zpool_shrink+0xab/0x3a0
 zswap_frontswap_store+0x10b/0x610
...
WARNING: CPU: 1 PID: 92 at mm/z3fold.c:278 release_z3fold_page_locked+0x25/0x40
Modules linked in:
...
INFO: rcu_preempt self-detected stall on CPU
	2-...!: (20958 ticks this GP) idle=5da/1/4611686018427387906
	softirq=4104/4113 fqs=11 
...
RIP: 0010:queued_spin_lock_slowpath+0x132/0x190
RSP: 0000:ffffb12740db7750 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
RAX: 0000000000100101 RBX: ffff9cbc7a7000c8 RCX: 0000000000000001
RDX: 0000000000000101 RSI: 0000000000000001 RDI: 0000000000000101
RBP: 0000000000000000 R08: ffff9cbc7fc21240 R09: ffffffffaf19c900
R10: ffffb12740db75a0 R11: 0000000000000010 R12: fffff00480522d20
R13: ffff9cbc548b4000 R14: ffff9cbc7a7000d8 R15: fffff00480522d00
 ? __zswap_pool_current+0x80/0x90
 z3fold_zpool_shrink+0x1d3/0x3a0
 zswap_frontswap_store+0x10b/0x610
...

With lock debugging enabled, the log is a bit different, but similar.

BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48  max: 48!
48 locks held by memory-eater/619:
 #0: 000000002da807ce (&mm->mmap_sem){++++}, at: __do_page_fault+0x122/0x5a0
 #1: 0000000012fa6629 (&(&pool->lock)->rlock#3){+.+.}, at: z3fold_zpool_shrink+0x47/0x3e0
 #2: 00000000c85f45dd (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
 #3: 00000000876f5fdc (&(&zhdr->page_lock)->rlock){+.+.}, at: z3fold_zpool_shrink+0xb7/0x3e0
...
watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [memory-eater:613]
Modules linked in:
irq event stamp: 1435394
hardirqs last  enabled at (1435393): [<ffffffff9b90ed81>]
_raw_spin_unlock_irqrestore+0x51/0x60
hardirqs last disabled at (1435394): [<ffffffff9b907baa>] __schedule+0xba/0xbb0
softirqs last  enabled at (1434508): [<ffffffff9bc0027c>] __do_softirq+0x27c/0x516
softirqs last disabled at (1434323): [<ffffffff9b069a29>] irq_exit+0xa9/0xc0
CPU: 0 PID: 613 Comm: memory-eater Tainted: G        W
4.16.0-yocto-standard+ #9
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1 04/01/2014
RIP: 0010:queued_spin_lock_slowpath+0x177/0x1a0
RSP: 0000:ffffa61f80e074e0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000000 RBX: ffff9704379cba08 RCX: ffff97043fc22080
RDX: 0000000000000001 RSI: ffffffff9c05f6a0 RDI: 0000000000040000
RBP: 0000000000000000 R08: ffffffff9b1f2215 R09: 0000000000000000
R10: ffffa61f80e07490 R11: ffff9704379cba20 R12: ffff97043fc22080
R13: ffffde77404e0920 R14: ffff970413824000 R15: ffff9704379cba00
FS:  00007f8c6317f700(0000) GS:ffff97043fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8c43f3d010 CR3: 000000003aba0000 CR4: 00000000000006f0
Call Trace:
 do_raw_spin_lock+0xad/0xb0
 z3fold_zpool_malloc+0x595/0x790
...

The problem is easy to reproduce. Please see [2] and the other files
at [3] for details. Various additional crash logs, observed with
chromeos-4.14, are available at [4].

Please let me know if there is anything else I can do to help solving
or debugging the problem. I had a look into the code, but I must admit
that its locking is a mystery to me.

Thanks,
Guenter

---
[1] http://server.roeck-us.net/qemu/z3pool/crashdump
[2] http://server.roeck-us.net/qemu/z3pool/README
[3] http://server.roeck-us.net/qemu/z3pool/
[4] https://bugs.chromium.org/p/chromium/issues/detail?id=822360