Hi,
On Sat, Oct 10, 2020 at 09:49:35AM +0800, yang_y_yi wrote:
> Olivier, thank you so much for helping figure out this, it does work
> as the code you changed, so we can fix the issue without this patch
> series. My question is can it also work for normal mbuf or indirect
> mbuf? (I mean pkt is direct mbuf or indirect mbuf)
Yes, it works for any mbuf type for pkt (direct, indirect, ext).
Happy to see it solves your issue!
Regards,
Olivier
> At 2020-10-09 19:55:25, "Olivier Matz" <olivier.m...@6wind.com> wrote:
> >Hi,
> >
> >On Fri, Oct 09, 2020 at 05:51:23PM +0800, yang_y_yi wrote:
> >> Olivier, thank you so much for your reply, your patch post for vhost help
> >> me understand your concern better, I totally agree. For GSO case, let me
> >> show you a simple code to explain my issue.
> >>
> >>
> >>
> >>
> >>
> >> struct rte_mbuf *pkt = rte_pktmbuf_alloc(mp);
> >> virtio_dev_extbuf_alloc(pkt, data_len)
> >> struct rte_mbuf * pkt_seg1 = rte_pktmbuf_alloc(indirect_pool);
> >>
> >>
> >> rte_pktmbuf_attach(pkt_seg1, pkt);
> >> rte_mbuf_ext_refcnt_update(pkt, -1);
> >>
> >> struct rte_mbuf * pkt_seg2 = rte_pktmbuf_alloc(indirect_pool);
> >> rte_pktmbuf_attach(pkt_seg2, pkt);
> >> rte_mbuf_ext_refcnt_update(pkt, -1);
> >> struct rte_mbuf *pkt_segs[2] = {pkt_seg1, pkt_seg2};
> >>
> >> rte_eth_tx_burst(dev->port_id, qid, pkt_segs, 2);
> >>
> >>
> >> Is it a simple test you expect? The issue here is nobody explicitly calls
> >> rte_pktmbuf_free(pkt), rte_pktmbuf_free(pkt_segX) in PMD driver won't free
> >> "pkt", Is it clear to you now?
> >
> >
> >Thank you for the small code. Yes, this is what I expected.
> >
> >The proper way to do this is something like this:
> >
> > /* create a mbuf, and attach it to an external buffer */
> > struct rte_mbuf *pkt = rte_pktmbuf_alloc(mp);
> > virtio_dev_extbuf_alloc(pkt, data_len)
> >
> > /* create a new mbuf, attach it to the previous one: the resulting
> > * mbuf is also an "external mbuf" (is has the EXT_ATTACHED_MBUF
> > * flag, and its data is stored in the ext buffer.
> > * See an example here: https://www.droids-corp.org/~zer0/ext-mbuf.svg
> > */
> > struct rte_mbuf *pkt_seg1 = rte_pktmbuf_alloc(indirect_pool);
> > rte_pktmbuf_attach(pkt_seg1, pkt);
> >
> > /* do the same another time */
> > struct rte_mbuf *pkt_seg2 = rte_pktmbuf_alloc(indirect_pool);
> > rte_pktmbuf_attach(pkt_seg2, pkt);
> >
> > /* release the original pkt, we don't need it anymore */
> > rte_pktmbuf_free(pkt);
> >
> > /* send the new segments, they will be freed by the driver once
> > * Tx is done. When the last packet referencing the external buffer
> > * is freed, the free callback of the buffer will be invoked. */
> > struct rte_mbuf *pkt_segs[2] = {pkt_seg1, pkt_seg2};
> > rte_eth_tx_burst(dev->port_id, qid, pkt_segs, 2);
> >
> >Hope this is clearer now.
> >
> >Regards,
> >Olivier
> >
> >
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> At 2020-10-07 17:48:21, "Olivier Matz" <olivier.m...@6wind.com> wrote:
> >> >Hi,
> >> >
> >> >On Sun, Sep 27, 2020 at 01:55:21PM +0800, yang_y_yi wrote:
> >> >> Per GSO requirement, this is a must-have change, Jiayu, can you help
> >> >> review
> >> >> this series?
> >> >
> >> >I can't ack this patch until I have a simple and clear test case (only
> >> >with mbuf functions, without GSO or vhost) showing the issue we have
> >> >today with current.
> >> >
> >> >> Olivier, if you used the old interface, maybe you need to change your
> >> >> code to
> >> >> adapt this, I don't think we can have a better way to handle GSO case.
> >> >
> >> >Sorry, I don't get your point. What do I need to change in which code?
> >> >
> >> >(some more comments below)
> >> >
> >> >> At 2020-08-04 09:31:19, "yang_y_yi" <yang_y...@163.com> wrote:
> >> >>
> >> >> At 2020-08-03 20:34:25, "Olivier Matz" <olivier.m...@6wind.com> wrote:
> >> >> >On Mon, Aug 03, 2020 at 05:42:13PM +0800, yang_y_yi wrote:
> >> >> >> At 2020-08-03 16:11:39, "Olivier Matz" <olivier.m...@6wind.com>
> >> >> >> wrote:
> >> >> >> >On Mon, Aug 03, 2020 at 09:26:40AM +0800, yang_y_yi wrote:
> >> >> >> >> At 2020-08-03 04:29:07, "Olivier Matz" <olivier.m...@6wind.com>
> >> >> >> >> wrote:
> >> >> >> >> >Hi,
> >> >> >> >> >
> >> >> >> >> >On Sun, Aug 02, 2020 at 07:12:36AM +0800, yang_y_yi wrote:
> >> >> >> >> >>
> >> >> >> >> >>
> >> >> >> >> >> At 2020-07-31 23:15:43, "Olivier Matz"
> >> >> >> >> >> <olivier.m...@6wind.com> wrote:
> >> >> >> >> >> >Hi,
> >> >> >> >> >> >
> >> >> >> >> >> >On Thu, Jul 30, 2020 at 08:08:59PM +0800, yang_y...@163.com
> >> >> >> >> >> >wrote:
> >> >> >> >> >> >> From: Yi Yang <yangy...@inspur.com>
> >> >> >> >> >> >>
> >> >> >> >> >> >> In GSO case, segmented mbufs are attached to original
> >> >> >> >> >> >> mbuf which can't be freed when it is external. The issue
> >> >> >> >> >> >> is free_cb doesn't know original mbuf and doesn't free
> >> >> >> >> >> >> it when refcnt of shinfo is 0.
> >> >> >> >> >> >>
> >> >> >> >> >> >> Original mbuf can be freed by rte_pktmbuf_free segmented
> >> >> >> >> >> >> mbufs or by rte_pktmbuf_free original mbuf. Two kind of
> >> >> >> >> >> >> cases should have different behaviors. free_cb won't
> >> >> >> >> >> >> explicitly call rte_pktmbuf_free to free original mbuf
> >> >> >> >> >> >> if it is freed by rte_pktmbuf_free original mbuf, but it
> >> >> >> >> >> >> has to call rte_pktmbuf_free to free original mbuf if it
> >> >> >> >> >> >> is freed by rte_pktmbuf_free segmented mbufs.
> >> >> >> >> >> >>
> >> >> >> >> >> >> In order to fix this issue, free_cb interface has to been
> >> >> >> >> >> >> changed, __rte_pktmbuf_free_extbuf must deliver called
> >> >> >> >> >> >> mbuf pointer to free_cb, argument opaque can be defined
> >> >> >> >> >> >> as a custom struct by user, it can includes original mbuf
> >> >> >> >> >> >> pointer, user-defined free_cb can compare caller mbuf with
> >> >> >> >> >> >> mbuf in opaque struct, free_cb should free original mbuf
> >> >> >> >> >> >> if they are not same, this corresponds to rte_pktmbuf_free
> >> >> >> >> >> >> segmented mbufs case, otherwise, free_cb won't free original
> >> >> >> >> >> >> mbuf because the caller explicitly called rte_pktmbuf_free
> >> >> >> >> >> >> to free it.
> >> >> >> >> >> >>
> >> >> >> >> >> >> Here is pseduo code to show two kind of cases.
> >> >> >> >> >> >>
> >> >> >> >> >> >> case 1. rte_pktmbuf_free segmented mbufs
> >> >> >> >> >> >>
> >> >> >> >> >> >> nb_tx = rte_gso_segment(original_mbuf, /* original mbuf */
> >> >> >> >> >> >> &gso_ctx,
> >> >> >> >> >> >> /* segmented mbuf */
> >> >> >> >> >> >> (struct rte_mbuf **)&gso_mbufs,
> >> >> >> >> >> >> MAX_GSO_MBUFS);
> >> >> >> >> >> >
> >> >> >> >> >> >I'm sorry but it is not very clear to me what operations are
> >> >> >> >> >> >done by
> >> >> >> >> >> >rte_gso_segment().
> >> >> >> >> >> >
> >> >> >> >> >> >In the current code, I only see calls to rte_pktmbuf_attach(),
> >> >> >> >> >> >which do not deal with external buffers. Am I missing
> >> >> >> >> >> >something?
> >> >> >> >> >> >
> >> >> >> >> >> >Are you able to show the issue only with mbuf functions? It
> >> >> >> >> >> >would
> >> >> >> >> >> >be helpful to understand what does not work.
> >> >> >> >> >> >
> >> >> >> >> >> >
> >> >> >> >> >> >Thanks,
> >> >> >> >> >> >Olivier
> >> >> >> >> >> >
> >> >> >> >> >> Oliver, thank you for comment, let me show you why it doesn't
> >> >> >> >> >> work for my use case. In OVS DPDK, VM uses vhostuserclient to
> >> >> >> >> >> send large packets whose size is about 64K because we enabled
> >> >> >> >> >> TSO & UFO, these large packets use rte_mbufs allocated by DPDK
> >> >> >> >> >> virtio_net function
> >> >> >> >> >> virtio_dev_pktmbuf_alloc() (in file
> >> >> >> >> >> lib/librte_vhost/virtio_net.c. Please refer to [PATCH V1 3/3],
> >> >> >> >> >> I changed free_cb as below, these packets use the same
> >> >> >> >> >> allocate function and the same free_cb no matter they are TCP
> >> >> >> >> >> packet or UDP packets, in case of VXLAN TSO, most NICs can't
> >> >> >> >> >> support inner UDP fragment offload, so OVS DPDK has to do it
> >> >> >> >> >> by software, for UDP case, the original rte_mbuf only can be
> >> >> >> >> >> freed by segmented rte_mbufs which are output packets of
> >> >> >> >> >> rte_gso_segment, i.e. the original rte_mbuf only can freed by
> >> >> >> >> >> free_cb, you can see, it explicitly called
> >> >> >> >> >> rte_pktmbuf_free(arg->mbuf), the condition statement "if
> >> >> >> >> >> (caller_m != arg->mbuf)" is true for this case, this has no
> >> >> >> >> >> problem, but for TCP case, the original mbuf is delivered to
> >> >> >> >> >> rte_eth_tx_burst() but not segmented rte_mbufs output by
> >> >> >> >> >> rte_gso_segment, PMD driver will call
> >> >> >> >> >> rte_pktmbuf_free(original_rte_mbuf) but not
> >> >> >> >> >> rte_pktmbuf_free(segmented_rte_mbufs), the same free_cb will
> >> >> >> >> >> be called, that means original_rte_mbuf will be freed twice,
> >> >> >> >> >> you know what will happen, this is just the issue I'm fixing.
> >> >> >> >> >> I bring in caller_m argument, it can help work around this
> >> >> >> >> >> because caller_m is arg->mbuf and the condition statement "if
> >> >> >> >> >> (caller_m != arg->mbuf)" is false, you can't fix it without
> >> >> >> >> >> the change this patch series did.
> >> >> >> >> >
> >> >> >> >> >I'm sill not sure to get your issue. Please, if you have a
> >> >> >> >> >simple test
> >> >> >> >> >case using only mbufs functions (without virtio, gso, ...), it
> >> >> >> >> >would be
> >> >> >> >> >very helpful because we will be sure that we are talking about
> >> >> >> >> >the same
> >> >> >> >> >thing. In case there is an issue, it can easily become a unit
> >> >> >> >> >test.
> >> >> >> >>
> >> >> >> >> Oliver, I think you don't get the point, free operation can't be
> >> >> >> >> controlled by the application itself,
> >> >> >> >> it is done by PMD driver and triggered by rte_eth_tx_burst, I
> >> >> >> >> have shown pseudo code,
> >> >> >> >> rte_gso_segment just segments a large mbuf to multiple mbufs, it
> >> >> >> >> won't send them, the application
> >> >> >> >> will call rte_eth_tx_burst to send them finally.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> >That said, I looked at vhost mbuf allocation and gso
> >> >> >> >> >segmentation, and
> >> >> >> >> >I found some strange things:
> >> >> >> >> >
> >> >> >> >> >1/ In virtio_dev_extbuf_alloc(), and I there are 2 paths to
> >> >> >> >> >create the
> >> >> >> >> > ext mbuf.
> >> >> >> >> >
> >> >> >> >> > a/ The first one stores the shinfo struct in the mbuf,
> >> >> >> >> > basically
> >> >> >> >> > like this:
> >> >> >> >> >
> >> >> >> >> > pkt = rte_pktmbuf_alloc(mp);
> >> >> >> >> > shinfo = rte_pktmbuf_mtod(pkt, struct rte_mbuf_ext_shared_info
> >> >> >> >> > *);
> >> >> >> >> > buf = rte_malloc(NULL, buf_len, RTE_CACHE_LINE_SIZE);
> >> >> >> >> > shinfo->free_cb = virtio_dev_extbuf_free;
> >> >> >> >> > shinfo->fcb_opaque = buf;
> >> >> >> >> > rte_mbuf_ext_refcnt_set(shinfo, 1);
> >> >> >> >> >
> >> >> >> >> > I don't think it is a good idea, because there is no
> >> >> >> >> > guarantee that
> >> >> >> >> > the mbuf won't be freed before the buffer. For instance,
> >> >> >> >> > doing
> >> >> >> >> > this will probably fail:
> >> >> >> >> >
> >> >> >> >> > pkt2 = rte_pktmbuf_alloc(mp);
> >> >> >> >> > rte_pktmbuf_attach(pkt2, pkt);
> >> >> >> >> > rte_pktmbuf_free(pkt); /* pkt is freed, but it contains shinfo
> >> >> >> >> > ! */
> >> >> >> >>
> >> >> >> >> pkt is created by the application I can control, so I can control
> >> >> >> >> it where it will be freed, right?
> >> >> >> >
> >> >> >> >This example shows that mbufs allocated like this by the vhost
> >> >> >> >driver are not constructed correctly. If an application attach a new
> >> >> >> >packet (pkt2) to it and frees the original one (pkt), it may result
> >> >> >> >in a
> >> >> >> >memory corruption.
> >> >> >> >
> >> >> >> >Of course, to be tested and confirmed.
> >> >> >>
> >> >> >> No, attach will increase refcnt of shinfo, free_cb only is called
> >> >> >> when refcnt of shinfo is decreased to
> >> >> >> 0, isn't it?
> >> >> >
> >> >> >When pkt will be freed, it will decrement the shinfo refcnt, and
> >> >> >after it will be 1. So the buffer won't be freed. After that, the
> >> >> >mbuf pkt will be detached, and will return to the mbuf pool. It means
> >> >> >it can be reallocated, and the next user can overwrite shinfo which
> >> >> >is still stored in the mbuf data.
> >> >>
> >> >> I think this is an issue of DPDK itself, if external buffer in shinfo
> >> >> is freed, shinfo should be set to NULL, if user will
> >> >> overwrite it, he/she should use the same way as a new external buffer
> >> >> is attached.
> >> >
> >> >No, there is no issue in DPDK. The lifetime of shinfo should be at least
> >> >the same the lifetime of the buffer. If shinfo is stored in initial mbuf
> >> >(called "pkt" in the example above), the mbuf and shinfo can be freed
> >> >while
> >> >the buffer is still in use by another packet.
> >> >
> >> >> >I did a test to show it, see:
> >> >> >http://git.droids-corp.org/?p=dpdk.git;a=commitdiff;h=a617494eeb01ff
> >> >> >
> >> >> >If you run the mbuf autotest, it segfaults.
> >> >>
> >> >> I think your test is wrong, you're changing shinfo (which is being
> >> >> used) in wrong way, if free_bc is NULL, it will be invalid.
> >> >
> >> >I'm changing the data of a newly allocated mbuf, it is perfectly legal.
> >> >I happens that it points the the shinfo that is still in use.
> >> >
> >> >
> >> >>
> >> >> static inline void
> >> >> rte_pktmbuf_attach_extbuf(struct rte_mbuf *m, void *buf_addr,
> >> >> rte_iova_t buf_iova, uint16_t buf_len,
> >> >> struct rte_mbuf_ext_shared_info *shinfo)
> >> >> {
> >> >> /* mbuf should not be read-only */
> >> >> RTE_ASSERT(RTE_MBUF_DIRECT(m) && rte_mbuf_refcnt_read(m) == 1);
> >> >> RTE_ASSERT(shinfo->free_cb != NULL);
> >> >>
> >> >> For any shinfo operation, you should do it by
> >> >> rte_pktmbuf_attach_extbuf, you can't change it at will after that.
> >> >>
> >> >> >
> >> >> >
> >> >> >>
> >> >> >> >
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> > To do this properly, the mbuf refcnt should be increased,
> >> >> >> >> > and
> >> >> >> >> > the mbuf should be freed in the callback. But I don't
> >> >> >> >> > think it's
> >> >> >> >> > worth doing it, given the second path (b/) looks good to
> >> >> >> >> > me.
> >> >> >> >> >
> >> >> >> >> > b/ The second path stores the shinfo struct at the end of the
> >> >> >> >> > allocated buffer, like this:
> >> >> >> >> >
> >> >> >> >> > pkt = rte_pktmbuf_alloc(mp);
> >> >> >> >> > buf_len += sizeof(*shinfo) + sizeof(uintptr_t);
> >> >> >> >> > buf_len = RTE_ALIGN_CEIL(total_len, sizeof(uintptr_t));
> >> >> >> >> > buf = rte_malloc(NULL, buf_len, RTE_CACHE_LINE_SIZE);
> >> >> >> >> > shinfo = rte_pktmbuf_ext_shinfo_init_helper(buf, &buf_len,
> >> >> >> >> > virtio_dev_extbuf_free,
> >> >> >> >> > buf);
> >> >> >> >> >
> >> >> >> >> > I think this is correct, because we have the guarantee
> >> >> >> >> > that shinfo
> >> >> >> >> > exists as long as the buffer exists.
> >> >> >> >>
> >> >> >> >> What buffer does the allocated buffer you're saying here? The
> >> >> >> >> issue we're discussing how we can
> >> >> >> >> free original mbuf which owns shinfo buffer.
> >> >> >> >
> >> >> >> >I don't get your question.
> >> >> >> >
> >> >> >> >I'm just saying that this code path looks correct, compared to
> >> >> >> >the previous one.
> >> >> >>
> >> >> >> I think you're challenging principle of external mbuf, that isn't
> >> >> >> the thing I address.
> >> >> >
> >> >> >I'm not challenging anything, I'm saying there is a bug in this code,
> >> >> >and the unit test above tends to confirm it.
> >> >>
> >> >> If it is bug, you can post a patch to fix it, it isn't related with my
> >> >> patches. But in my opinion, you don't
> >> >> use it in correct way, I don't think it is a bug.
> >> >
> >> >I'll submit a patch for this.
> >> >
> >> >The point is you are testing GSO on top of wrongly-constructed mbufs, so
> >> >it would be safer for you to fix this before doing more tests.
> >> >
> >> >
> >> >> >> >> >2/ in rte_gso_segment(), there is a loop like this:
> >> >> >> >> >
> >> >> >> >> > while (pkt_seg) {
> >> >> >> >> > rte_mbuf_refcnt_update(pkt_seg, -1);
> >> >> >> >> > pkt_seg = pkt_seg->next;
> >> >> >> >> > }
> >> >> >> >> >
> >> >> >> >> > You change it to take in account the refcnt for ext mbufs.
> >> >> >> >> >
> >> >> >> >> > I may have missed something but I wonder why it is not simply:
> >> >> >> >> >
> >> >> >> >> > rte_pktmbuf_free(pkt_seg);
> >> >> >> >> >
> >> >> >> >> > It will decrease the proper refcnt, and free the mbufs if they
> >> >> >> >> > are not used.
> >> >> >> >>
> >> >> >> >> Again, rte_gso_segment just decreases refcnt by one, this will
> >> >> >> >> ensure the last segmented
> >> >> >> >> mbuf free will trigger freeing original mbuf (only free_cb can do
> >> >> >> >> this).
> >> >> >> >
> >> >> >> >rte_pktmbuf_free() will also decerase the refcnt, and free the
> >> >> >> >resources
> >> >> >> >when the refcnt reaches 0.
> >> >> >> >
> >> >> >> >It has some advantages compared to decrease the reference counter
> >> >> >> >of all
> >> >> >> >segments:
> >> >> >> >
> >> >> >> >- no need to iterate the segments, there is only one function call
> >> >> >> >- no need to have a special case for ext mbufs like you did in your
> >> >> >> >patch
> >> >> >> >- it may be safer, in case some segments have a refcnt == 1, because
> >> >> >> > resources will be freed.
> >> >> >>
> >> >> >> For external mbuf, attach only increases refcnt of shinfo, refcnt of
> >> >> >> mbuf won't be touched. For normal
> >> >> >> mbuf, attach only increase refcnt of mbuf, no shinfo there, no
> >> >> >> refcnt of shinfo increased.
> >> >> >
> >> >> >I suppose rte_gso_segment() can take any mbuf type as input: standard
> >> >> >mbuf, indirect mbuf, ext mbuf, or even a mbuf chaing containing
> >> >> >segments of
> >> >> >different types.
> >> >> >
> >> >> >For instance, if you pass a chain of 2 mbufs:
> >> >> >- the first one is a direct mbuf containing the IP/TCP headers
> >> >> >(orig_hdr)
> >> >> >- the second on is a mbuf pointing to an ext buffer (orig_payload)
> >> >> >
> >> >> >I expect that the resulting mbuf after calling gso contains a list of
> >> >> >mbufs
> >> >> >like this:
> >> >> >- a first segment containing the IP/TCP headers (new_hdr)
> >> >> >- a payload segment pointing on the same ext buffer
> >> >> >
> >> >> >In theory, there is no reason that orig_hdr should be referenced by
> >> >> >another new mbuf, because it only contains headers (no data). If that's
> >> >> >the case, its refcnt is 1, and decreasing it to 0 without freeing it
> >> >> >is a bug.
> >> >>
> >> >> For this user scenario, orig_m is owner of external buffer, small
> >> >> segmented mbufs reference
> >> >> it, you shouldn't free orig_m before all attached segmented mbufs are
> >> >> freed, isn't it?
> >> >
> >> >In this case, orig_hdr has to be freed because it is a direct mbuf (not
> >> >shared).
> >> >The buffer pointed by orig_payload will be freed when all newly created
> >> >segments are freed.
> >> >
> >> >
> >> >> >
> >> >> >Anyway, there is maybe no issue in that case, but I was just suggesting
> >> >> >that using rte_pktmbuf_free() is easier to read, and safer than
> >> >> >manually
> >> >> >decreasing the refcnt of each segment.
> >> >> >
> >> >> >
> >> >> >> >> >Again, sorry if this is not the issue your are referring to, but
> >> >> >> >> >in this case I really think that having a simple example code
> >> >> >> >> >that
> >> >> >> >> >shows the issue would help.
> >> >> >> >>
> >> >> >> >> Oliver, my statement in the patch I sent out has pseudo code to
> >> >> >> >> show this. I don't think a simple
> >> >> >> >> unit test can show it.
> >> >> >> >
> >> >> >> >I don't see why. The PMDs and the libraries use the mbuf functions,
> >> >> >> >why
> >> >> >> >a unit test couldn't call the same functions?
> >> >> >> >
> >> >> >> >> Let me summarize it here again. For original mbuf, there are two
> >> >> >> >> cases freeing
> >> >> >> >> it, case one is PMD driver calls free against segmented mbufs,
> >> >> >> >> last segmented mbuf free will trigger
> >> >> >> >> free_cb call which will free original large & extended mbuf.
> >> >> >> >
> >> >> >> >OK
> >> >> >> >
> >> >> >> >> Case two is PMD driver will call free against
> >> >> >> >> original mbuf, that also will call free_cb to free attached
> >> >> >> >> extended buffer.
> >> >> >> >
> >> >> >> >OK
> >> >> >> >
> >> >> >> >And what makes that case 1 or case 2 is executed?
> >> >> >> >
> >> >> >> >> In case one free_cb must call
> >> >> >> >> rte_pktmbuf_free otherwise nobody will free original large &
> >> >> >> >> extended mbuf, in case two free_cb can't
> >> >> >> >> call rte_pktmbuf_free because the caller calling it is just
> >> >> >> >> rte_pktmbuf_free we need. That is to say, you
> >> >> >> >> must use the same free_cb to handle these two cases, this is my
> >> >> >> >> issue and the point you don't get.
> >> >> >> >
> >> >> >> >I think there is no need to change the free_cb API. It should work
> >> >> >> >like
> >> >> >> >this:
> >> >> >> >
> >> >> >> >- virtio creates the original external mbuf (orig_m)
> >> >> >> >- gso will create a new mbuf referencing the external buffer (new_m)
> >> >> >> >
> >> >> >> >At this point, the shinfo has a refcnt of 2. The large buffer will
> >> >> >> >be
> >> >> >> >freed as soon as rte_pktmbuf_free() is called on orig_m and new_m,
> >> >> >> >whatever the order.
> >> >> >> >
> >> >> >> >Regards,
> >> >> >> >Olivier
> >> >> >>
> >> >> >> Oliver, the reason it works is I changed free_cb API, case 1 doesn't
> >> >> >> know orig_m, how you make it free orig_m in free_cb.
> >> >> >> The intention I change free_cb is to let it know orig_m, I saw OVS
> >> >> >> DPDK ran out out buffers and orig_m isn't freed, that is why
> >> >> >> I want to bring in this to fix the issue. Again, in case 1, nobody
> >> >> >> explicitly calls ret_pktmbuf_free(orig_m) except free_cb I changed.
> >> >> >
> >> >> >If nobody calls ret_pktmbuf_free(orig_m), it is a problem.
> >> >> >The free_cb is to free the buffer, not the mbuf.
> >> >> >
> >> >> >To me, it should work like this:
> >> >> >
> >> >> >1- virtio creates a mbuf attached to the ext buffer (the shinfo
> >> >> >placement
> >> >> > bug should be fixed)
> >> >> >2- gso create mbufs that reference the the same ext buf (by attaching
> >> >> >the
> >> >> > new mbuf)
> >> >> >3- gso must free the original mbuf
> >> >>
> >> >> This is impossible, segmented mbufs are referencing external buffer in
> >> >> original mbuf,
> >> >> how do you free it? As I said rte_gso_segment has no way to free it,
> >> >> please tell me a way if
> >> >> you know how to do this.
> >> >
> >> >As I said above, calling rte_mbuf_free(orig_m) will decrement the
> >> >reference
> >> >counters on all segments. The segments will be returned to the pool if the
> >> >refcnt reaches 0.
> >> >
> >> >>
> >> >> >4- the PMD transmits the new mbufs, and frees them
> >> >> >
> >> >> >Whatever 3- or 4- is executed first, at the end we are sure that:
> >> >> >- all mbufs will be returned to the pool
> >> >> >- the linear buffer will be freed when the refcnt reaches 0.
> >> >> >
> >> >> >If this is still unclear, please, write a unit test like I did
> >> >> >above to show your issue.
> >> >> >
> >> >> >Regards,
> >> >> >Olivier
> >> >> >
> >> >>
> >> >> The issue is in "3- gso must free the original mbuf",
> >> >> rte_pktmbuf_free(segmented_mbus) can't do it,
> >> >> rte_gso_segment is impossible to do it, only feasible point is free_cb,
> >> >> please let me know if you have
> >> >> a better way to free original mbuf and don't impact on segmented mbufs
> >> >> in PMD. My point is you must
> >> >> have a place to call rte_pktmbuf_free(rogin_m) explicitly, otherwise it
> >> >> is impossible to return it to memory
> >> >> pool, please point out where it can be called in my user scenario. I
> >> >> don't care how it is done, I just care it can
> >> >> fix my issue, please don't hesitate and send me a patch if you can,
> >> >> thanks a lot.
> >> >
> >> >Sorry, but I don't see how I can be clearer to what I explained
> >> >in my previous answer.
> >> >
> >> >Please, *provide a simple test example* without gso/vhost, and I can help
> >> >to make it work.
> >> >
> >> >
> >> >Regards,
> >> >Olivier
> >> >
> >> >
> >> >> >
> >> >> >
> >> >> >> free_cb must handle case 1 and case 2 in the same code, for case 1,
> >> >> >> caller_m is segmented new_m, for case 2, caller_m is orig_m.
> >> >> >>
> >> >> >> loop in rte_gso_segement is handling original mbuf (this mbuf is
> >> >> >> multi-mbuf and includes multiple mbufs which are linked by next
> >> >> >> pointer), it isn't a problem at all.
> >> >> >>
> >> >> >> Please show me code how you can fix my issue if you don't change
> >> >> >> free_cb, thank you.
> >> >> >>
> >> >> >> struct shinfo_arg {
> >> >> >> void *buf;
> >> >> >> struct rte_mbuf *mbuf;
> >> >> >> };
> >> >> >>
> >> >> >> virtio_dev_extbuf_free(struct rte_mbuf *caller_m, void *opaque)
> >> >> >> {
> >> >> >> struct shinfo_arg *arg = (struct shinfo_arg *)opaque;
> >> >> >>
> >> >> >> rte_free(arg->buf);
> >> >> >> if (caller_m != arg->mbuf)
> >> >> >> rte_pktmbuf_free(arg->mbuf);
> >> >> >> rte_free(arg);
> >> >> >> }
