[Qemu-devel] [PATCH] blockjob: update nodes head while removing all bdrv

[Qemu-devel] [PATCH] blockjob: update nodes head while removing all bdrv

[Sergio Lopez]

block_job_remove_all_bdrv() iterates through job->nodes, calling
bdrv_root_unref_child() for each entry. The call to the latter may
reach child_job_[can_]set_aio_ctx(), which will also attempt to
traverse job->nodes, potentially finding entries that where freed
on previous iterations.

To avoid this situation, update job->nodes head on each iteration to
ensure that already freed entries are no longer linked to the list.

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1746631
Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 blockjob.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/blockjob.c b/blockjob.c
index 6e32d1a0c0..7b1551d981 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -192,6 +192,12 @@ void block_job_remove_all_bdrv(BlockJob *job)
         BdrvChild *c = l->data;
         bdrv_op_unblock_all(c->bs, job->blocker);
         bdrv_root_unref_child(c);
+        /*
+         * The call above may reach child_job_[can_]set_aio_ctx(), which will
+         * also traverse job->nodes, so update the head here to make sure it
+         * doesn't attempt to process an already freed BdrvChild.
+         */
+        job->nodes = l->next;
     }
     g_slist_free(job->nodes);
     job->nodes = NULL;
-- 
2.21.0

Re: [Qemu-devel] [PATCH] blockjob: update nodes head while removing all bdrv

[Max Reitz]

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On 10.09.19 13:07, Sergio Lopez wrote:
> block_job_remove_all_bdrv() iterates through job->nodes, calling
> bdrv_root_unref_child() for each entry. The call to the latter may
> reach child_job_[can_]set_aio_ctx(), which will also attempt to
> traverse job->nodes, potentially finding entries that where freed
> on previous iterations.
> 
> To avoid this situation, update job->nodes head on each iteration to
> ensure that already freed entries are no longer linked to the list.
> 
> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1746631
> Signed-off-by: Sergio Lopez <slp@redhat.com>
> ---
>  blockjob.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/blockjob.c b/blockjob.c
> index 6e32d1a0c0..7b1551d981 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -192,6 +192,12 @@ void block_job_remove_all_bdrv(BlockJob *job)
>          BdrvChild *c = l->data;
>          bdrv_op_unblock_all(c->bs, job->blocker);
>          bdrv_root_unref_child(c);
> +        /*
> +         * The call above may reach child_job_[can_]set_aio_ctx(), which will
> +         * also traverse job->nodes, so update the head here to make sure it
> +         * doesn't attempt to process an already freed BdrvChild.
> +         */
> +        job->nodes = l->next;
>      }
>      g_slist_free(job->nodes);

But this will leak the whole list.

Max

>      job->nodes = NULL;
> 



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Re: [Qemu-devel] [PATCH] blockjob: update nodes head while removing all bdrv

[Sergio Lopez]

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Max Reitz <mreitz@redhat.com> writes:

> On 10.09.19 13:07, Sergio Lopez wrote:
>> block_job_remove_all_bdrv() iterates through job->nodes, calling
>> bdrv_root_unref_child() for each entry. The call to the latter may
>> reach child_job_[can_]set_aio_ctx(), which will also attempt to
>> traverse job->nodes, potentially finding entries that where freed
>> on previous iterations.
>> 
>> To avoid this situation, update job->nodes head on each iteration to
>> ensure that already freed entries are no longer linked to the list.
>> 
>> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1746631
>> Signed-off-by: Sergio Lopez <slp@redhat.com>
>> ---
>>  blockjob.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/blockjob.c b/blockjob.c
>> index 6e32d1a0c0..7b1551d981 100644
>> --- a/blockjob.c
>> +++ b/blockjob.c
>> @@ -192,6 +192,12 @@ void block_job_remove_all_bdrv(BlockJob *job)
>>          BdrvChild *c = l->data;
>>          bdrv_op_unblock_all(c->bs, job->blocker);
>>          bdrv_root_unref_child(c);
>> +        /*
>> +         * The call above may reach child_job_[can_]set_aio_ctx(), which will
>> +         * also traverse job->nodes, so update the head here to make sure it
>> +         * doesn't attempt to process an already freed BdrvChild.
>> +         */
>> +        job->nodes = l->next;
>>      }
>>      g_slist_free(job->nodes);
>
> But this will leak the whole list.

Ouch. This is what happens when you rush up things. I'll send a v2 ASAP.

Thanks,
Sergio.

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