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5ca2e29f68
The panic can be reproduced by executing the command:
./bench sockmap -c 2 -p 1 -a --rx-verdict-ingress --rx-strp 100000
Then a kernel panic was captured:
'''
[ 657.460555] kernel BUG at net/core/skbuff.c:2178!
[ 657.462680] Tainted: [W]=WARN
[ 657.463287] Workqueue: events sk_psock_backlog
...
[ 657.469610] <TASK>
[ 657.469738] ? die+0x36/0x90
[ 657.469916] ? do_trap+0x1d0/0x270
[ 657.470118] ? pskb_expand_head+0x612/0xf40
[ 657.470376] ? pskb_expand_head+0x612/0xf40
[ 657.470620] ? do_error_trap+0xa3/0x170
[ 657.470846] ? pskb_expand_head+0x612/0xf40
[ 657.471092] ? handle_invalid_op+0x2c/0x40
[ 657.471335] ? pskb_expand_head+0x612/0xf40
[ 657.471579] ? exc_invalid_op+0x2d/0x40
[ 657.471805] ? asm_exc_invalid_op+0x1a/0x20
[ 657.472052] ? pskb_expand_head+0xd1/0xf40
[ 657.472292] ? pskb_expand_head+0x612/0xf40
[ 657.472540] ? lock_acquire+0x18f/0x4e0
[ 657.472766] ? find_held_lock+0x2d/0x110
[ 657.472999] ? __pfx_pskb_expand_head+0x10/0x10
[ 657.473263] ? __kmalloc_cache_noprof+0x5b/0x470
[ 657.473537] ? __pfx___lock_release.isra.0+0x10/0x10
[ 657.473826] __pskb_pull_tail+0xfd/0x1d20
[ 657.474062] ? __kasan_slab_alloc+0x4e/0x90
[ 657.474707] sk_psock_skb_ingress_enqueue+0x3bf/0x510
[ 657.475392] ? __kasan_kmalloc+0xaa/0xb0
[ 657.476010] sk_psock_backlog+0x5cf/0xd70
[ 657.476637] process_one_work+0x858/0x1a20
'''
The panic originates from the assertion BUG_ON(skb_shared(skb)) in
skb_linearize(). A previous commit(see Fixes tag) introduced skb_get()
to avoid race conditions between skb operations in the backlog and skb
release in the recvmsg path. However, this caused the panic to always
occur when skb_linearize is executed.
The "--rx-strp 100000" parameter forces the RX path to use the strparser
module which aggregates data until it reaches 100KB before calling sockmap
logic. The 100KB payload exceeds MAX_MSG_FRAGS, triggering skb_linearize.
To fix this issue, just move skb_get into sk_psock_skb_ingress_enqueue.
'''
sk_psock_backlog:
sk_psock_handle_skb
skb_get(skb) <== we move it into 'sk_psock_skb_ingress_enqueue'
sk_psock_skb_ingress____________
↓
|
| → sk_psock_skb_ingress_self
| sk_psock_skb_ingress_enqueue
sk_psock_verdict_apply_________________↑ skb_linearize
'''
Note that for verdict_apply path, the skb_get operation is unnecessary so
we add 'take_ref' param to control it's behavior.
Fixes: a454d84ee2 ("bpf, sockmap: Fix skb refcnt race after locking changes")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/r/20250407142234.47591-4-jiayuan.chen@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>