l2tp_ip6_sendmsg needs to avoid accounting for the transport header
twice when splicing more data into an already partially-occupied skbuff.
To manage this, we check whether the skbuff contains data using
skb_queue_empty when deciding how much data to append using
ip6_append_data.
However, the code which performed the calculation was incorrect:
ulen = len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0;
...due to C operator precedence, this ends up setting ulen to
transhdrlen for messages with a non-zero length, which results in
corrupted packets on the wire.
Add parentheses to correct the calculation in line with the original
intent.
Fixes: 9d4c75800f61 ("ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data()")
Cc: David Howells <dhowells(a)redhat.com>
Cc: stable(a)vger.kernel.org
Signed-off-by: Tom Parkin <tparkin(a)katalix.com>
---
This issue was uncovered by Debian build-testing for the
golang-github-katalix-go-l2tp package[1].
It seems 9d4c75800f61 has been backported to the linux-6.1.y stable
kernel (and possibly others), so I think this fix will also need
backporting.
The bug is currently seen on at least Debian Bookworm, Ubuntu Jammy, and
Debian testing/unstable.
Unfortunately tests using "ip l2tp" and which focus on dataplane
transport will not uncover this bug: it's necessary to send a packet
using an L2TPIP6 socket opened by userspace, and to verify the packet on
the wire. The l2tp-ktest[2] test suite has been extended to cover this.
[1]. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1063746
[2]. https://github.com/katalix/l2tp-ktest
---
net/l2tp/l2tp_ip6.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index dd3153966173..7bf14cf9ffaa 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -627,7 +627,7 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
back_from_confirm:
lock_sock(sk);
- ulen = len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0;
+ ulen = len + (skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0);
err = ip6_append_data(sk, ip_generic_getfrag, msg,
ulen, transhdrlen, &ipc6,
&fl6, (struct rt6_info *)dst,
--
2.34.1
Hi,
this series does basically two things:
1. Disables automatic load balancing as adviced by the hardware
workaround.
2. Forces the sharing of the load submitted to CCS among all the
CCS available (as of now only DG2 has more than one CCS). This
way the user, when sending a query, will see only one CCS
available.
Andi
Andi Shyti (2):
drm/i915/gt: Disable HW load balancing for CCS
drm/i915/gt: Set default CCS mode '1'
drivers/gpu/drm/i915/gt/intel_gt.c | 11 +++++++++++
drivers/gpu/drm/i915/gt/intel_gt_regs.h | 3 +++
drivers/gpu/drm/i915/gt/intel_workarounds.c | 6 ++++++
drivers/gpu/drm/i915/i915_drv.h | 17 +++++++++++++++++
drivers/gpu/drm/i915/i915_query.c | 5 +++--
5 files changed, 40 insertions(+), 2 deletions(-)
--
2.43.0
Commit fb24ea52f78e0d595852e ("drivers: Remove explicit invocations of
mmiowb()") remove all mmiowb() in drivers, but it says:
"NOTE: mmiowb() has only ever guaranteed ordering in conjunction with
spin_unlock(). However, pairing each mmiowb() removal in this patch with
the corresponding call to spin_unlock() is not at all trivial, so there
is a small chance that this change may regress any drivers incorrectly
relying on mmiowb() to order MMIO writes between CPUs using lock-free
synchronisation."
The mmio in radeon_ring_commit() is protected by a mutex rather than a
spinlock, but in the mutex fastpath it behaves similar to spinlock and
need a mmiowb() to make sure the wptr is up-to-date for hardware.
Without this, we get such an error when run 'glxgears' on weak ordering
architectures such as LoongArch:
radeon 0000:04:00.0: ring 0 stalled for more than 10324msec
radeon 0000:04:00.0: ring 3 stalled for more than 10240msec
radeon 0000:04:00.0: GPU lockup (current fence id 0x000000000001f412 last fence id 0x000000000001f414 on ring 3)
radeon 0000:04:00.0: GPU lockup (current fence id 0x000000000000f940 last fence id 0x000000000000f941 on ring 0)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
radeon 0000:04:00.0: scheduling IB failed (-35).
[drm:radeon_gem_va_ioctl [radeon]] *ERROR* Couldn't update BO_VA (-35)
Cc: stable(a)vger.kernel.org
Signed-off-by: Tianyang Zhang <zhangtianyang(a)loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai(a)loongson.cn>
---
drivers/gpu/drm/radeon/radeon_ring.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/radeon/radeon_ring.c b/drivers/gpu/drm/radeon/radeon_ring.c
index 38048593bb4a..d461dc85d820 100644
--- a/drivers/gpu/drm/radeon/radeon_ring.c
+++ b/drivers/gpu/drm/radeon/radeon_ring.c
@@ -183,6 +183,7 @@ void radeon_ring_commit(struct radeon_device *rdev, struct radeon_ring *ring,
if (hdp_flush && rdev->asic->mmio_hdp_flush)
rdev->asic->mmio_hdp_flush(rdev);
radeon_ring_set_wptr(rdev, ring);
+ mmiowb(); /* Make sure wptr is up-to-date for hw */
}
/**
--
2.43.0
On 2024/2/20 13:32, Kairui Song wrote:
> On Tue, Feb 20, 2024 at 12:49 PM Chengming Zhou <zhouchengming(a)bytedance.com>
> wrote:
>>
>> On 2024/2/20 06:10, Barry Song wrote:
>>> On Mon, Feb 19, 2024 at 9:21 PM Kairui Song <ryncsn(a)gmail.com> wrote:
>>>>
>>>> From: Kairui Song <kasong(a)tencent.com>
>>>>
>>>> When skipping swapcache for SWP_SYNCHRONOUS_IO, if two or more threads
>>>> swapin the same entry at the same time, they get different pages (A,
> B).
>>>> Before one thread (T0) finishes the swapin and installs page (A)
>>>> to the PTE, another thread (T1) could finish swapin of page (B),
>>>> swap_free the entry, then swap out the possibly modified page
>>>> reusing the same entry. It breaks the pte_same check in (T0) because
>>>> PTE value is unchanged, causing ABA problem. Thread (T0) will
>>>> install a stalled page (A) into the PTE and cause data corruption.
>>>>
>>>> One possible callstack is like this:
>>>>
>>>> CPU0 CPU1
>>>> ---- ----
>>>> do_swap_page() do_swap_page() with same entry
>>>> <direct swapin path> <direct swapin path>
>>>> <alloc page A> <alloc page B>
>>>> swap_read_folio() <- read to page A swap_read_folio() <- read to page
> B
>>>> <slow on later locks or interrupt> <finished swapin first>
>>>> .. set_pte_at()
>>>> swap_free() <- entry is free
>>>> <write to page B, now page A
> stalled>
>>>> <swap out page B to same swap
> entry>
>>>> pte_same() <- Check pass, PTE seems
>>>> unchanged, but page A
>>>> is stalled!
>>>> swap_free() <- page B content lost!
>>>> set_pte_at() <- staled page A installed!
>>>>
>>>> And besides, for ZRAM, swap_free() allows the swap device to discard
>>>> the entry content, so even if page (B) is not modified, if
>>>> swap_read_folio() on CPU0 happens later than swap_free() on CPU1,
>>>> it may also cause data loss.
>>>>
>>>> To fix this, reuse swapcache_prepare which will pin the swap entry
> using
>>>> the cache flag, and allow only one thread to swap it in, also prevent
>>>> any parallel code from putting the entry in the cache. Release the pin
>>>> after PT unlocked.
>>>>
>>>> Racers just loop and wait since it's a rare and very short event.
>>>> A schedule_timeout_uninterruptible(1) call is added to avoid repeated
>>>> page faults wasting too much CPU, causing livelock or adding too much
>>>> noise to perf statistics. A similar livelock issue was described in
>>>> commit 029c4628b2eb ("mm: swap: get rid of livelock in swapin
> readahead")
>>>>
>>>> Reproducer:
>>>>
>>>> This race issue can be triggered easily using a well constructed
>>>> reproducer and patched brd (with a delay in read path) [1]:
>>>>
>>>> With latest 6.8 mainline, race caused data loss can be observed easily:
>>>> $ gcc -g -lpthread test-thread-swap-race.c && ./a.out
>>>> Polulating 32MB of memory region...
>>>> Keep swapping out...
>>>> Starting round 0...
>>>> Spawning 65536 workers...
>>>> 32746 workers spawned, wait for done...
>>>> Round 0: Error on 0x5aa00, expected 32746, got 32743, 3 data loss!
>>>> Round 0: Error on 0x395200, expected 32746, got 32743, 3 data loss!
>>>> Round 0: Error on 0x3fd000, expected 32746, got 32737, 9 data loss!
>>>> Round 0 Failed, 15 data loss!
>>>>
>>>> This reproducer spawns multiple threads sharing the same memory region
>>>> using a small swap device. Every two threads updates mapped pages one
> by
>>>> one in opposite direction trying to create a race, with one dedicated
>>>> thread keep swapping out the data out using madvise.
>>>>
>>>> The reproducer created a reproduce rate of about once every 5 minutes,
>>>> so the race should be totally possible in production.
>>>>
>>>> After this patch, I ran the reproducer for over a few hundred rounds
>>>> and no data loss observed.
>>>>
>>>> Performance overhead is minimal, microbenchmark swapin 10G from 32G
>>>> zram:
>>>>
>>>> Before: 10934698 us
>>>> After: 11157121 us
>>>> Cached: 13155355 us (Dropping SWP_SYNCHRONOUS_IO flag)
>>>>
>>>> Fixes: 0bcac06f27d7 ("mm, swap: skip swapcache for swapin of
> synchronous device")
>>>> Link:
> https://github.com/ryncsn/emm-test-project/tree/master/swap-stress-race [1]
>>>> Reported-by: "Huang, Ying" <ying.huang(a)intel.com>
>>>> Closes:
> https://lore.kernel.org/lkml/87bk92gqpx.fsf_-_@yhuang6-desk2.ccr.corp.intel…
>>>> Signed-off-by: Kairui Song <kasong(a)tencent.com>
>>>> Cc: stable(a)vger.kernel.org
>>>>
>>>> ---
>>>> V3:
> https://lore.kernel.org/all/20240216095105.14502-1-ryncsn@gmail.com/
>>>> Update from V3:
>>>> - Use schedule_timeout_uninterruptible(1) for now instead of
> schedule() to
>>>> prevent the busy faulting task holds CPU and livelocks [Huang, Ying]
>>>>
>>>> V2:
> https://lore.kernel.org/all/20240206182559.32264-1-ryncsn@gmail.com/
>>>> Update from V2:
>>>> - Add a schedule() if raced to prevent repeated page faults wasting CPU
>>>> and add noise to perf statistics.
>>>> - Use a bool to state the special case instead of reusing existing
>>>> variables fixing error handling [Minchan Kim].
>>>>
>>>> V1: https://lore.kernel.org/all/20240205110959.4021-1-ryncsn@gmail.com/
>>>> Update from V1:
>>>> - Add some words on ZRAM case, it will discard swap content on
> swap_free
>>>> so the race window is a bit different but cure is the same. [Barry
> Song]
>>>> - Update comments make it cleaner [Huang, Ying]
>>>> - Add a function place holder to fix CONFIG_SWAP=n built [SeongJae
> Park]
>>>> - Update the commit message and summary, refer to SWP_SYNCHRONOUS_IO
>>>> instead of "direct swapin path" [Yu Zhao]
>>>> - Update commit message.
>>>> - Collect Review and Acks.
>>>>
>>>> include/linux/swap.h | 5 +++++
>>>> mm/memory.c | 20 ++++++++++++++++++++
>>>> mm/swap.h | 5 +++++
>>>> mm/swapfile.c | 13 +++++++++++++
>>>> 4 files changed, 43 insertions(+)
>>>>
>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>>>> index 4db00ddad261..8d28f6091a32 100644
>>>> --- a/include/linux/swap.h
>>>> +++ b/include/linux/swap.h
>>>> @@ -549,6 +549,11 @@ static inline int swap_duplicate(swp_entry_t swp)
>>>> return 0;
>>>> }
>>>>
>>>> +static inline int swapcache_prepare(swp_entry_t swp)
>>>> +{
>>>> + return 0;
>>>> +}
>>>> +
>>>> static inline void swap_free(swp_entry_t swp)
>>>> {
>>>> }
>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>> index 7e1f4849463a..a99f5e7be9a5 100644
>>>> --- a/mm/memory.c
>>>> +++ b/mm/memory.c
>>>> @@ -3799,6 +3799,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>>>> struct page *page;
>>>> struct swap_info_struct *si = NULL;
>>>> rmap_t rmap_flags = RMAP_NONE;
>>>> + bool need_clear_cache = false;
>>>> bool exclusive = false;
>>>> swp_entry_t entry;
>>>> pte_t pte;
>>>> @@ -3867,6 +3868,20 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>>>> if (!folio) {
>>>> if (data_race(si->flags & SWP_SYNCHRONOUS_IO) &&
>>>> __swap_count(entry) == 1) {
>>>> + /*
>>>> + * Prevent parallel swapin from proceeding with
>>>> + * the cache flag. Otherwise, another thread
> may
>>>> + * finish swapin first, free the entry, and
> swapout
>>>> + * reusing the same entry. It's undetectable as
>>>> + * pte_same() returns true due to entry reuse.
>>>> + */
>>>> + if (swapcache_prepare(entry)) {
>>>> + /* Relax a bit to prevent rapid
> repeated page faults */
>>>> + schedule_timeout_uninterruptible(1);
>>>
>>> Not a ideal model, imaging two tasks,
>>>
>>> task A - low priority running on a LITTLE core
>>> task B - high priority and have real-time requirements such as audio,
>>> graphics running on a big core.
>>>
>>> The original code will make B win even if it is a bit later than A as
> its CPU is
>>> much faster to finish swap_read_folio for example from zRAM. task B's
>>> swap-in can finish very soon.
>>>
>>> With the patch, B will wait a tick and its real-time performance will be
>>> negatively affected from time to time once low priority and high
> priority
>>> tasks fault in the same PTE and high priority tasks are a bit later than
>>> low priority tasks. This is a kind of priority inversion.
>>>
>>> When we support large folio swap-in, things can get worse. For example,
>>> to swap-in 16 or even more pages in one do_swap_page, the chance for
>>> task A and task B located in the same range of 16 PTEs will increase
>>> though they are not located in the same PTE.
>>>
>>> Please consider this is not a blocker for this patch. But I will put
> the problem
>>> in my list and run some real tests on Android phones later.
>>
>> Good point. Late for the discussion, I'm wondering why not get an extra
> reference
>> on the swap entry, instead of swapcache_prepare()? Then the faster thread
> will
>> succeed, but can't free the swap entry. Later, the slower thread will
> find the
>> changed pte value and fail, and free the swap entry. Maybe I missed
> something?
>
> Hi, Chengming
>
> That was my initial purpose. Then found a lot of problems with it. Increase
> swap count here, it may race with another swap free and end up increasing
> the swap count of a freed entry.
>
> That can be fixed with audits and new helpers, but there are many other
> potential issues too. One major problem is that after count bump, raced
> swap threads will fallback to cached swap in. Pages in swapcache can be
> swaped out without allocating an entry, making the problem we were trying
> to resolve more serious.
Thanks for your clarification! Right, there are many issues I just ignored...