On 8/5/26 4:22 PM, Nnamdi Onyeyiri wrote:
> On Tue, Jul 21, 2026 at 11:38:05PM +0100, Nnamdi Onyeyiri wrote:
>> Spurious wakeups in tcp_msg_wait_data() aren't being handled by
>> tcp_bpf_recvmsg() and tcp_bpf_recvmsg_parser(), leading to unexpected
>> EAGAIN errors returned by recvfrom()/recv().  Adding handling for the
>> wakeup and a selftest.
>>
>> This issue was first discovered in an application that adds sockets to
>> a sockmap as a way to view the received data.  No redirects or any
>> other operations are performed.
>>
>> Sashiko has noted a few other pre-existing issues in the same area
>> (https://patch.msgid.link/20260714205118.17DB11F000E9@smtp.kernel.org)
>> that can lead to EAGAIN in tcp_bpf_recvmsg() and
>> tcp_bpf_recvmsg_parser().  A local run of Sashiko also identified a
>> potential issue in tcp_bpf_recvmsg() handling zero-data FIN packets when
>> the MSG_PEEK flag is set.  To prevent this patchset from growing too
>> large, I intend to submit follow up patches to address these once this
>> one has been accepted.
>>
>> Changes in v7:
>> - In tcp_bpf_recvmsg check for data in the TCP_CLOSE, !timeo and
>>    signal_pending branches.
>> - Refactored changes to tcp_bpf_recvmsg to reduce duplication.
>> - Increase the number of iterations in the selftests.
>> - Documented selftests numeric constants.
>> - Link to v6: https://patch.msgid.link/20260720171535.67867-1-nnamdio@gmail.com
>>
>> Changes in v6:
>> - Closing the file descriptor in the selftest worker thread.
>> - Ensuring the selftest loop breaks early for an error in the worker
>>    thread.
>> - Added comments to selftest regarding focus on EAGAIN error.
>> - Updated selftest commit message to imperative mood.
>> - Link to v5: https://patch.msgid.link/20260717155348.54975-1-nnamdio@gmail.com
>>
>> Changes in v5:
>> - Move selftest from net into bpf/prog_tests/sockmap_basic.c
>> - Link to v4: https://patch.msgid.link/20260715213538.37229-1-nnamdio@gmail.com
>>
>> Changes in v4:
>> - Fix potential data loss in tcp_bpf_recvmsg() when a FIN or RST has
>>    been received.
>> - Check the return code of pthread_create() in the selftest.
>> - Fix race caused by using EXPECT macros in a thread in selftest.
>> - Link to v3: https://patch.msgid.link/20260714203927.32289-1-nnamdio@gmail.com
>>
>> Changes in v3:
>> - Added the sockmap_recvfrom selftest.
>> - Link to v2: https://patch.msgid.link/alFRK66z45eDNZA7@localhost.localdomain
>>
>> Changes in v2:
>> - In tcp_bpf_recvmsg, handle signals and the socket closing in the loop.
>> - Fix spurious wakeups when SO_RCVTIMEO has been set on the socket.
>> - Link to v1: https://patch.msgid.link/ak_rR-Skd8Mvn4mH@localhost.localdomain
>>
>> Signed-off-by: Nnamdi Onyeyiri <nnamdio@gmail.com>
>> ---
>> Nnamdi Onyeyiri (2):
>>    bpf, sockmap: handle spurious tcp_msg_wait_data() wakeup
>>    selftests/bpf: add sockmap recvfrom EAGAIN selftest
>>
>>   net/ipv4/tcp_bpf.c                            |  72 ++++++++--
>>   .../selftests/bpf/prog_tests/sockmap_basic.c  | 136 ++++++++++++++++++
>>   2 files changed, 199 insertions(+), 9 deletions(-)
>>
>> -- 
>> 2.52.0
>>
> Hi all, just wondering if you need anything more from me on this?


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>


targeting bpf-next without Fixes tags seems fine given the scope