ACK: [SRU][N][PATCH 0/1] nvmet-tcp: Fix a possible sporadic response drops in weakly ordered arch

[Ian Whitfield]

On Tue, May 06, 2025 at 04:11:50PM +0300, Ioanna Alifieraki wrote:
> BugLink: https://bugs.launchpad.net/bugs/2106381
> 
> [Impact]
> 
> A user reported a bug in nvme over tcp driver affecting aarch64 architectures.
> In weakly ordered architectures the compiler can reorder the instructions reading/setting
> queue->cmd and queue->rcv_state which can lead to dropping IOs and IO hanging.
> 
> The bug has been fixed upstream in [1], introduced in 6.14.
> 
> [Test Plan]
> The bug is reproducible on arm64 architectures.
> Setup nvme over tcp.
> 
> Using an arm based machien as the target run a fio test with the following config:
> 
> [global]
> ioengine=libaio
> max_latency=45s
> end_fsync=1
> create_serialize=0
> size=3200m
> directory=/path/to/storage
> ramp_time=30
> lat_percentiles=1
> direct=1
> filename_format=fiodata.$jobnum
> verify_dump=1
> numjobs=16
> fallocate=native
> stonewall=1
> group_reporting=1
> file_service_type=random
> iodepth=16
> runtime=5m
> time_based=1
> [random_0_100_4k]
> bs=4k
> rw=randwrite
> 
> [Where problems could occur]
> To fix the bug the patch reads/writes queue->cmd with READ/WRITE_ONCE
> statements and queue->rcv_state with smp_load_acquire and smp_store_release.
> The patch modifies the nvme-tcp driver and therefore any potential regressions
> regard setups using nvme over tpc.
> 
> [Other Info]
> 
> The user is able to reproduce the issue with kernles 5.19(no longer supported), 6.8 and 6.11.
> 
> For 6.11 Oracular the patch is pulled in as part of upstream stable patchset 2025-04-15, LP #2107437, https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2107437
> 
> [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/nvme?id=a16f88964c647103dad7743a484b216d488a6352
> 
> 
> Meir Elisha (1):
>   nvmet-tcp: Fix a possible sporadic response drops in weakly ordered
>     arch
> 
>  drivers/nvme/target/tcp.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> -- 
> 2.34.1
> 
> 
> -- 
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Acked-by: Ian Whitfield <ian.whitfield at canonical.com>