* FAILED: patch "[PATCH] mptcp: avoid deadlock on fallback while reinjecting" failed to apply to 6.1-stable tree
@ 2025-12-29 12:36 gregkh
2025-12-30 13:20 ` [PATCH 6.1.y] mptcp: avoid deadlock on fallback while reinjecting Sasha Levin
0 siblings, 1 reply; 2+ messages in thread
From: gregkh @ 2025-12-29 12:36 UTC (permalink / raw)
To: pabeni, kuba, matttbe; +Cc: stable
The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x ffb8c27b0539dd90262d1021488e7817fae57c42
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025122942-stonework-habitant-a877@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From ffb8c27b0539dd90262d1021488e7817fae57c42 Mon Sep 17 00:00:00 2001
From: Paolo Abeni <pabeni@redhat.com>
Date: Fri, 5 Dec 2025 19:55:17 +0100
Subject: [PATCH] mptcp: avoid deadlock on fallback while reinjecting
Jakub reported an MPTCP deadlock at fallback time:
WARNING: possible recursive locking detected
6.18.0-rc7-virtme #1 Not tainted
--------------------------------------------
mptcp_connect/20858 is trying to acquire lock:
ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_try_fallback+0xd8/0x280
but task is already holding lock:
ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&msk->fallback_lock);
lock(&msk->fallback_lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by mptcp_connect/20858:
#0: ff1100001da18290 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_sendmsg+0x114/0x1bc0
#1: ff1100001db40fd0 (k-sk_lock-AF_INET#2){+.+.}-{0:0}, at: __mptcp_retrans+0x2cb/0xaa0
#2: ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0
stack backtrace:
CPU: 0 UID: 0 PID: 20858 Comm: mptcp_connect Not tainted 6.18.0-rc7-virtme #1 PREEMPT(full)
Hardware name: Bochs, BIOS Bochs 01/01/2011
Call Trace:
<TASK>
dump_stack_lvl+0x6f/0xa0
print_deadlock_bug.cold+0xc0/0xcd
validate_chain+0x2ff/0x5f0
__lock_acquire+0x34c/0x740
lock_acquire.part.0+0xbc/0x260
_raw_spin_lock_bh+0x38/0x50
__mptcp_try_fallback+0xd8/0x280
mptcp_sendmsg_frag+0x16c2/0x3050
__mptcp_retrans+0x421/0xaa0
mptcp_release_cb+0x5aa/0xa70
release_sock+0xab/0x1d0
mptcp_sendmsg+0xd5b/0x1bc0
sock_write_iter+0x281/0x4d0
new_sync_write+0x3c5/0x6f0
vfs_write+0x65e/0xbb0
ksys_write+0x17e/0x200
do_syscall_64+0xbb/0xfd0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7fa5627cbc5e
Code: 4d 89 d8 e8 14 bd 00 00 4c 8b 5d f8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 11 c9 c3 0f 1f 80 00 00 00 00 48 8b 45 10 0f 05 <c9> c3 83 e2 39 83 fa 08 75 e7 e8 13 ff ff ff 0f 1f 00 f3 0f 1e fa
RSP: 002b:00007fff1fe14700 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fa5627cbc5e
RDX: 0000000000001f9c RSI: 00007fff1fe16984 RDI: 0000000000000005
RBP: 00007fff1fe14710 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff1fe16920
R13: 0000000000002000 R14: 0000000000001f9c R15: 0000000000001f9c
The packet scheduler could attempt a reinjection after receiving an
MP_FAIL and before the infinite map has been transmitted, causing a
deadlock since MPTCP needs to do the reinjection atomically from WRT
fallback.
Address the issue explicitly avoiding the reinjection in the critical
scenario. Note that this is the only fallback critical section that
could potentially send packets and hit the double-lock.
Reported-by: Jakub Kicinski <kuba@kernel.org>
Closes: https://netdev-ctrl.bots.linux.dev/logs/vmksft/mptcp-dbg/results/412720/1-mptcp-join-sh/stderr
Fixes: f8a1d9b18c5e ("mptcp: make fallback action and fallback decision atomic")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251205-net-mptcp-misc-fixes-6-19-rc1-v1-4-9e4781a6c1b8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index d8a7f7029164..9b1fafd87cb9 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2769,10 +2769,13 @@ static void __mptcp_retrans(struct sock *sk)
/*
* make the whole retrans decision, xmit, disallow
- * fallback atomic
+ * fallback atomic, note that we can't retrans even
+ * when an infinite fallback is in progress, i.e. new
+ * subflows are disallowed.
*/
spin_lock_bh(&msk->fallback_lock);
- if (__mptcp_check_fallback(msk)) {
+ if (__mptcp_check_fallback(msk) ||
+ !msk->allow_subflows) {
spin_unlock_bh(&msk->fallback_lock);
release_sock(ssk);
goto clear_scheduled;
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [PATCH 6.1.y] mptcp: avoid deadlock on fallback while reinjecting
2025-12-29 12:36 FAILED: patch "[PATCH] mptcp: avoid deadlock on fallback while reinjecting" failed to apply to 6.1-stable tree gregkh
@ 2025-12-30 13:20 ` Sasha Levin
0 siblings, 0 replies; 2+ messages in thread
From: Sasha Levin @ 2025-12-30 13:20 UTC (permalink / raw)
To: stable; +Cc: Paolo Abeni, Jakub Kicinski, Matthieu Baerts (NGI0), Sasha Levin
From: Paolo Abeni <pabeni@redhat.com>
[ Upstream commit ffb8c27b0539dd90262d1021488e7817fae57c42 ]
Jakub reported an MPTCP deadlock at fallback time:
WARNING: possible recursive locking detected
6.18.0-rc7-virtme #1 Not tainted
--------------------------------------------
mptcp_connect/20858 is trying to acquire lock:
ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_try_fallback+0xd8/0x280
but task is already holding lock:
ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&msk->fallback_lock);
lock(&msk->fallback_lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by mptcp_connect/20858:
#0: ff1100001da18290 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_sendmsg+0x114/0x1bc0
#1: ff1100001db40fd0 (k-sk_lock-AF_INET#2){+.+.}-{0:0}, at: __mptcp_retrans+0x2cb/0xaa0
#2: ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0
stack backtrace:
CPU: 0 UID: 0 PID: 20858 Comm: mptcp_connect Not tainted 6.18.0-rc7-virtme #1 PREEMPT(full)
Hardware name: Bochs, BIOS Bochs 01/01/2011
Call Trace:
<TASK>
dump_stack_lvl+0x6f/0xa0
print_deadlock_bug.cold+0xc0/0xcd
validate_chain+0x2ff/0x5f0
__lock_acquire+0x34c/0x740
lock_acquire.part.0+0xbc/0x260
_raw_spin_lock_bh+0x38/0x50
__mptcp_try_fallback+0xd8/0x280
mptcp_sendmsg_frag+0x16c2/0x3050
__mptcp_retrans+0x421/0xaa0
mptcp_release_cb+0x5aa/0xa70
release_sock+0xab/0x1d0
mptcp_sendmsg+0xd5b/0x1bc0
sock_write_iter+0x281/0x4d0
new_sync_write+0x3c5/0x6f0
vfs_write+0x65e/0xbb0
ksys_write+0x17e/0x200
do_syscall_64+0xbb/0xfd0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7fa5627cbc5e
Code: 4d 89 d8 e8 14 bd 00 00 4c 8b 5d f8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 11 c9 c3 0f 1f 80 00 00 00 00 48 8b 45 10 0f 05 <c9> c3 83 e2 39 83 fa 08 75 e7 e8 13 ff ff ff 0f 1f 00 f3 0f 1e fa
RSP: 002b:00007fff1fe14700 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fa5627cbc5e
RDX: 0000000000001f9c RSI: 00007fff1fe16984 RDI: 0000000000000005
RBP: 00007fff1fe14710 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff1fe16920
R13: 0000000000002000 R14: 0000000000001f9c R15: 0000000000001f9c
The packet scheduler could attempt a reinjection after receiving an
MP_FAIL and before the infinite map has been transmitted, causing a
deadlock since MPTCP needs to do the reinjection atomically from WRT
fallback.
Address the issue explicitly avoiding the reinjection in the critical
scenario. Note that this is the only fallback critical section that
could potentially send packets and hit the double-lock.
Reported-by: Jakub Kicinski <kuba@kernel.org>
Closes: https://netdev-ctrl.bots.linux.dev/logs/vmksft/mptcp-dbg/results/412720/1-mptcp-join-sh/stderr
Fixes: f8a1d9b18c5e ("mptcp: make fallback action and fallback decision atomic")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251205-net-mptcp-misc-fixes-6-19-rc1-v1-4-9e4781a6c1b8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Adjust context ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/mptcp/protocol.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 10844f08752c..0d044ea1baeb 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2715,9 +2715,15 @@ static void __mptcp_retrans(struct sock *sk)
info.sent = 0;
info.limit = READ_ONCE(msk->csum_enabled) ? dfrag->data_len : dfrag->already_sent;
- /* make the whole retrans decision, xmit, disallow fallback atomic */
+ /*
+ * make the whole retrans decision, xmit, disallow
+ * fallback atomic, note that we can't retrans even
+ * when an infinite fallback is in progress, i.e. new
+ * subflows are disallowed.
+ */
spin_lock_bh(&msk->fallback_lock);
- if (__mptcp_check_fallback(msk)) {
+ if (__mptcp_check_fallback(msk) ||
+ !msk->allow_subflows) {
spin_unlock_bh(&msk->fallback_lock);
release_sock(ssk);
return;
--
2.51.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
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2025-12-29 12:36 FAILED: patch "[PATCH] mptcp: avoid deadlock on fallback while reinjecting" failed to apply to 6.1-stable tree gregkh
2025-12-30 13:20 ` [PATCH 6.1.y] mptcp: avoid deadlock on fallback while reinjecting Sasha Levin
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