padata: use integer wrap around to prevent deadlock on seq_nr overflow

Commit Message

VanGiang Nguyen Aug. 9, 2024, 6:21 a.m. UTC

When submitting more than 2^32 padata objects to padata_do_serial, the
current sorting implementation incorrectly sorts padata objects with
overflowed seq_nr, causing them to be placed before existing objects in
the reorder list. This leads to a deadlock in the serialization process
as padata_find_next cannot match padata->seq_nr and pd->processed
because the padata instance with overflowed seq_nr will be selected
next.

To fix this, we use an unsigned integer wrap around to correctly sort
padata objects in scenarios with integer overflow.

Co-developed-by: Christian Gafert <[e-mail]>
Signed-off-by: Christian Gafert <[e-mail]>
Co-developed-by: Max Ferger <[e-mail]>
Signed-off-by: Max Ferger <[e-mail]>
Signed-off-by: Van Giang Nguyen <[e-mail]>
---
 kernel/padata.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Daniel Jordan Aug. 13, 2024, 5 p.m. UTC | #1

Hello Van Giang,

On Fri, Aug 09, 2024 at 06:21:42AM GMT, VanGiang Nguyen wrote:
> When submitting more than 2^32 padata objects to padata_do_serial, the
> current sorting implementation incorrectly sorts padata objects with
> overflowed seq_nr, causing them to be placed before existing objects in
> the reorder list. This leads to a deadlock in the serialization process
> as padata_find_next cannot match padata->seq_nr and pd->processed
> because the padata instance with overflowed seq_nr will be selected
> next.
> 
> To fix this, we use an unsigned integer wrap around to correctly sort
> padata objects in scenarios with integer overflow.
> 

Could use a Fixes tag like this one:

Fixes: bfde23ce200e ("padata: unbind parallel jobs from specific CPUs")

Otherwise looks good, thanks.

Acked-by: Daniel Jordan <[e-mail]>

> Co-developed-by: Christian Gafert <[e-mail]>
> Signed-off-by: Christian Gafert <[e-mail]>
> Co-developed-by: Max Ferger <[e-mail]>
> Signed-off-by: Max Ferger <[e-mail]>
> Signed-off-by: Van Giang Nguyen <[e-mail]>
> ---
>  kernel/padata.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 53f4bc912712..222bccd0c96b 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -404,7 +404,8 @@ void padata_do_serial(struct padata_priv *padata)
>  	/* Sort in ascending order of sequence number. */
>  	list_for_each_prev(pos, &reorder->list) {
>  		cur = list_entry(pos, struct padata_priv, list);
> -		if (cur->seq_nr < padata->seq_nr)
> +		/* Compare by difference to consider integer wrap around */
> +		if ((signed int)(cur->seq_nr - padata->seq_nr) < 0)
>  			break;
>  	}
>  	list_add(&padata->list, pos);
> -- 
> 2.34.1
>

Herbert Xu Aug. 24, 2024, 1:42 p.m. UTC | #2

VanGiang Nguyen <[e-mail]> wrote:
> When submitting more than 2^32 padata objects to padata_do_serial, the
> current sorting implementation incorrectly sorts padata objects with
> overflowed seq_nr, causing them to be placed before existing objects in
> the reorder list. This leads to a deadlock in the serialization process
> as padata_find_next cannot match padata->seq_nr and pd->processed
> because the padata instance with overflowed seq_nr will be selected
> next.
> 
> To fix this, we use an unsigned integer wrap around to correctly sort
> padata objects in scenarios with integer overflow.
> 
> Co-developed-by: Christian Gafert <[e-mail]>
> Signed-off-by: Christian Gafert <[e-mail]>
> Co-developed-by: Max Ferger <[e-mail]>
> Signed-off-by: Max Ferger <[e-mail]>
> Signed-off-by: Van Giang Nguyen <[e-mail]>
> ---
> kernel/padata.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)

Patch applied.  Thanks.

Patch

diff --git a/kernel/padata.c b/kernel/padata.c
index 53f4bc912712..222bccd0c96b 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -404,7 +404,8 @@  void padata_do_serial(struct padata_priv *padata)
 	/* Sort in ascending order of sequence number. */
 	list_for_each_prev(pos, &reorder->list) {
 		cur = list_entry(pos, struct padata_priv, list);
-		if (cur->seq_nr < padata->seq_nr)
+		/* Compare by difference to consider integer wrap around */
+		if ((signed int)(cur->seq_nr - padata->seq_nr) < 0)
 			break;
 	}
 	list_add(&padata->list, pos);