Messages in this thread |  | | Date | Sun, 17 Jul 2022 07:49:12 -0700 | Subject | Re: [RFC] block: Add a NULL check in blk_mq_free_rqs() | From | Bart Van Assche <> |
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On 7/17/22 03:22, Gautam Menghani wrote: > Syzbot reported a general protection fault in the function > blk_mq_clear_rq_mapping() in the file block/blk-mq.c. > The issue is that the variable drv_tags is NULL, and this > originates from the struct blk_mq_tag_set. The dashboard link for this > issue is : > syzkaller.appspot.com/bug?id=c3ce4caa4fc58c156d4903984131cdfa38eee354 > > This patch fixes the above bug, but there is another syzbot bug which is > related to this and getting triggered after the call to > blk_mq_clear_rq_mapping(). As a result, I cannot determine if the issue > is really solved. The link to other issue: > syzkaller.appspot.com/bug?id=7643cea70f1d0ce15f5f4bc39488918837ad4233 > > Please provide feedback/suggestions on the same. > > Signed-off-by: Gautam Menghani <gautammenghani201@gmail.com> > --- > block/blk-mq.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 93d9d60980fb..c1dd1b78b95c 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -3092,7 +3092,8 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, > } > } > > - blk_mq_clear_rq_mapping(drv_tags, tags); > + if (drv_tags) > + blk_mq_clear_rq_mapping(drv_tags, tags); > > while (!list_empty(&tags->page_list)) { > page = list_first_entry(&tags->page_list, struct page, lru);
I don't see how drv_tags could be NULL without triggering a race condition. Please take a look at the nbd driver to see whether the root cause is perhaps in that driver instead of in the block layer core.
Thanks,
Bart.
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