From: Olivier Matz <olivier.matz@6wind.com>
To: Fengnan Chang <changfengnan@bytedance.com>
Cc: david.marchand@redhat.com, mb@smartsharesystems.com, dev@dpdk.org
Subject: Re: [PATCH v2] mempool: fix rte_mempool_avail_count may segment fault when used in multiprocess
Date: Tue, 22 Nov 2022 16:24:59 +0100 [thread overview]
Message-ID: <Y3zpy+WYve3l3d88@platinum> (raw)
In-Reply-To: <20221115123502.12560-1-changfengnan@bytedance.com>
Hi,
On Tue, Nov 15, 2022 at 08:35:02PM +0800, Fengnan Chang wrote:
> rte_mempool_create put tailq entry into rte_mempool_tailq list before
> populate, and pool_data set when populate. So in multi process, if
> process A create mempool, and process B can get mempool through
> rte_mempool_lookup before pool_data set, if B call rte_mempool_avail_count,
> it will cause segment fault.
>
> Fix this by put tailq entry into rte_mempool_tailq after populate.
>
> Signed-off-by: Fengnan Chang <changfengnan@bytedance.com>
> ---
> lib/mempool/rte_mempool.c | 43 ++++++++++++++++++++++-----------------
> 1 file changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
> index 4c78071a34..b3a6572fc8 100644
> --- a/lib/mempool/rte_mempool.c
> +++ b/lib/mempool/rte_mempool.c
> @@ -155,6 +155,27 @@ get_min_page_size(int socket_id)
> return wa.min == SIZE_MAX ? (size_t) rte_mem_page_size() : wa.min;
> }
>
> +static int
> +add_mempool_to_list(struct rte_mempool *mp)
> +{
> + struct rte_mempool_list *mempool_list;
> + struct rte_tailq_entry *te = NULL;
> +
> + /* try to allocate tailq entry */
> + te = rte_zmalloc("MEMPOOL_TAILQ_ENTRY", sizeof(*te), 0);
> + if (te == NULL) {
> + RTE_LOG(ERR, MEMPOOL, "Cannot allocate tailq entry!\n");
> + return -ENOMEM;
> + }
> +
> + te->data = mp;
> + mempool_list = RTE_TAILQ_CAST(rte_mempool_tailq.head, rte_mempool_list);
> + rte_mcfg_tailq_write_lock();
> + TAILQ_INSERT_TAIL(mempool_list, te, next);
> + rte_mcfg_tailq_write_unlock();
> +
> + return 0;
> +}
>
> static void
> mempool_add_elem(struct rte_mempool *mp, __rte_unused void *opaque,
> @@ -304,6 +325,9 @@ mempool_ops_alloc_once(struct rte_mempool *mp)
> if (ret != 0)
> return ret;
> mp->flags |= RTE_MEMPOOL_F_POOL_CREATED;
> + ret = add_mempool_to_list(mp);
> + if (ret != 0)
> + return ret;
One issue here is that if the rte_zmalloc("MEMPOOL_TAILQ_ENTRY") fails,
the function will fail, but rte_mempool_ops_alloc() may already be
successful.
I agree it's theorical, because an allocation failure would cause more
issues at the end. But, to be rigorous, I think we should do something
like this instead (not tested, just for the idea):
static int
mempool_ops_alloc_once(struct rte_mempool *mp)
{
struct rte_mempool_list *mempool_list;
struct rte_tailq_entry *te = NULL;
int ret;
/* only create the driver ops and add in tailq in if not already done */
if ((mp->flags & RTE_MEMPOOL_F_POOL_CREATED))
return 0;
te = rte_zmalloc("MEMPOOL_TAILQ_ENTRY", sizeof(*te), 0);
if (te == NULL) {
RTE_LOG(ERR, MEMPOOL, "Cannot allocate tailq entry!\n");
ret = -rte_errno;
goto fail;
}
te->data = mp;
mempool_list = RTE_TAILQ_CAST(rte_mempool_tailq.head, rte_mempool_list);
ret = rte_mempool_ops_alloc(mp);
if (ret != 0)
goto fail;
mp->flags |= RTE_MEMPOOL_F_POOL_CREATED;
rte_mcfg_tailq_write_lock();
TAILQ_INSERT_TAIL(mempool_list, te, next);
rte_mcfg_tailq_write_unlock();
return 0;
fail:
rte_free(te);
return ret;
}
Thinking a bit more about the problem itself: the segfault that you
describe could also happen in a primary, without multi-process:
- create an empty mempool
- call rte_mempool_avail_count() before it is populated
This simply means that an empty mempool is not ready for use, until
rte_mempool_set_ops_byname() or rte_mempool_populate*() is called. This
is something that we should document above the declaration of
rte_mempool_create_empty(). We could also say there that the mempool
will become visible to the secondary processes as soon as the driver ops
are set.
However I still believe that a better synchronization point is required
in the application. After all, the presence in the TAILQ does not give
any hint on the status of the object. Can we imagine a case where a
mempool is created empty in a primary, and populated in a secondary? If
such use-case exist, we may not want to take this patch.
> }
> return 0;
> }
> @@ -798,9 +822,7 @@ rte_mempool_create_empty(const char *name, unsigned n, unsigned elt_size,
> int socket_id, unsigned flags)
> {
> char mz_name[RTE_MEMZONE_NAMESIZE];
> - struct rte_mempool_list *mempool_list;
> struct rte_mempool *mp = NULL;
> - struct rte_tailq_entry *te = NULL;
> const struct rte_memzone *mz = NULL;
> size_t mempool_size;
> unsigned int mz_flags = RTE_MEMZONE_1GB|RTE_MEMZONE_SIZE_HINT_ONLY;
> @@ -820,8 +842,6 @@ rte_mempool_create_empty(const char *name, unsigned n, unsigned elt_size,
> RTE_CACHE_LINE_MASK) != 0);
> #endif
>
> - mempool_list = RTE_TAILQ_CAST(rte_mempool_tailq.head, rte_mempool_list);
> -
> /* asked for zero items */
> if (n == 0) {
> rte_errno = EINVAL;
> @@ -866,14 +886,6 @@ rte_mempool_create_empty(const char *name, unsigned n, unsigned elt_size,
> private_data_size = (private_data_size +
> RTE_MEMPOOL_ALIGN_MASK) & (~RTE_MEMPOOL_ALIGN_MASK);
>
> -
> - /* try to allocate tailq entry */
> - te = rte_zmalloc("MEMPOOL_TAILQ_ENTRY", sizeof(*te), 0);
> - if (te == NULL) {
> - RTE_LOG(ERR, MEMPOOL, "Cannot allocate tailq entry!\n");
> - goto exit_unlock;
> - }
> -
> mempool_size = RTE_MEMPOOL_HEADER_SIZE(mp, cache_size);
> mempool_size += private_data_size;
> mempool_size = RTE_ALIGN_CEIL(mempool_size, RTE_MEMPOOL_ALIGN);
> @@ -923,20 +935,13 @@ rte_mempool_create_empty(const char *name, unsigned n, unsigned elt_size,
> cache_size);
> }
>
> - te->data = mp;
> -
> - rte_mcfg_tailq_write_lock();
> - TAILQ_INSERT_TAIL(mempool_list, te, next);
> - rte_mcfg_tailq_write_unlock();
> rte_mcfg_mempool_write_unlock();
> -
> rte_mempool_trace_create_empty(name, n, elt_size, cache_size,
> private_data_size, flags, mp);
> return mp;
>
> exit_unlock:
> rte_mcfg_mempool_write_unlock();
> - rte_free(te);
> rte_mempool_free(mp);
> return NULL;
> }
> --
> 2.37.0 (Apple Git-136)
>
next prev parent reply other threads:[~2022-11-22 15:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-15 12:35 Fengnan Chang
2022-11-22 15:24 ` Olivier Matz [this message]
2022-11-29 9:57 ` [External] " Fengnan Chang
2023-07-17 16:43 ` Stephen Hemminger
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