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76fa42c004
__smbdirect_socket_schedule_cleanup() and smbdirect_socket_cleanup_work()
take sc->listen.lock and walk the listener's pending list, recursing
into smbdirect_socket_schedule_cleanup() for each child, and every
child takes its own listen.lock inside that walk.
This cannot deadlock for real: the nesting is strictly listener into
child, a child never listens, so the outer and the inner lock are
always different instances. lockdep only tracks lock classes, though;
it sees the same class acquired twice and reports a possible recursive
locking deadlock. This change therefore works around a lockdep
limitation rather than fixing a real hang, but the report is still
worth avoiding: lockdep disables itself after the first splat and then
hides real locking bugs for the rest of the run.
Only a socket that was a listener owns a populated listen.ready/pending
list; a child has empty lists and nothing to do in these blocks. Guard
both of them with sc->listen.backlog != -1, the "was a listener" marker
that smbdirect_socket_destroy() already uses: listen.backlog leaves its
initial -1 exactly once, when smbdirect_socket_listen() succeeds. The
alternative !sc->accept.listener test reads as "not a listener" while
meaning the opposite, and it is also true for an accepted child, whose
accept.listener has been cleared on hand-over. With the guard the walk
only runs for a listener and never nests a child's listen.lock under
it; a pending child stays on its listener's list for the free path
(smbdirect_socket_destroy) to reap.
[ 741.705044] WARNING: possible recursive locking detected
[ 741.705403] 7.1.0-next-20260623+ #75 Not tainted
[ 741.705695] --------------------------------------------
[ 741.706022] ksmbd.control/18502 is trying to acquire lock:
[ 741.706379] ffff888108d612f8 (&sc->listen.lock){....}-{3:3}, at: __smbdirect_socket_schedule_cleanup+0x719/0xd70
[ 741.707008]
[ 741.707008] but task is already holding lock:
[ 741.707396] ffff8881087642f8 (&sc->listen.lock){....}-{3:3}, at: __smbdirect_socket_schedule_cleanup+0x719/0xd70
[ 741.708025]
[ 741.708025] other info that might help us debug this:
[ 741.708448] Possible unsafe locking scenario:
[ 741.708448]
[ 741.708845] CPU0
[ 741.709016] ----
[ 741.709186] lock(&sc->listen.lock);
[ 741.709453] lock(&sc->listen.lock);
[ 741.709705]
[ 741.709705] *** DEADLOCK ***
[ 741.709705]
[ 741.710095] May be due to missing lock nesting notation
[ 741.710095]
[ 741.710663] 6 locks held by ksmbd.control/18502:
[ 741.710975] #0: ffff888109e51420 (sb_writers#7){.+.+}-{0:0}, at: vfs_write+0x1e7/0xc70
[ 741.711561] #1: ffff888126ec3880 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1be/0x4d0
[ 741.712147] #2: ffff888102af17b0 (kn->active#45){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x205/0x4d0
[ 741.712803] #3: ffffffff85ad1e00 (ctrl_lock){+.+.}-{4:4}, at: kill_server_store+0x1e0/0x2b0
[ 741.713381] #4: ffffffff85ad41a0 (init_lock){+.+.}-{4:4}, at: ksmbd_conn_transport_destroy+0x5b/0x3c0
[ 741.713995] #5: ffff8881087642f8 (&sc->listen.lock){....}-{3:3}, at: __smbdirect_socket_schedule_cleanup+0x719/0xd70
[ 741.714736]
[ 741.714736] stack backtrace:
[ 741.715038] CPU: 4 UID: 0 PID: 18502 Comm: ksmbd.control Not tainted 7.1.0-next-20260623+ #75 PREEMPT(lazy)
[ 741.715043] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 741.715046] Call Trace:
[ 741.715049] <TASK>
[ 741.715052] dump_stack_lvl+0x77/0xa0
[ 741.715058] print_deadlock_bug+0x279/0x290
[ 741.715065] __lock_acquire+0x272a/0x2e30
[ 741.715070] ? stack_trace_save+0xae/0x100
[ 741.715075] ? smb_direct_logging_vaprintf+0x1a0/0x230
[ 741.715079] ? __pfx_smb_direct_logging_vaprintf+0x10/0x10
[ 741.715082] ? __timer_delete+0x58/0x320
[ 741.715087] lock_acquire+0xd3/0x270
[ 741.715091] ? __smbdirect_socket_schedule_cleanup+0x719/0xd70
[ 741.715095] ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 741.715099] _raw_spin_lock_irqsave+0x42/0x60
[ 741.715105] ? __smbdirect_socket_schedule_cleanup+0x719/0xd70
Note the two addresses above: ffff888108d612f8 is the child's lock,
ffff8881087642f8 the listener's, always distinct objects.
Found with ksmbdzzer [2], a KSMBD fuzzer that drives libFuzzer with a
kcov-dataflow [1] coverage vector: it folds each instrumented
comparison/argument's runtime operand value together with its PC (the
default arm mixes them as pc⊕val) so that a new operand value at a known
site counts as new coverage.
[1] https://lwn.net/Articles/1077606/
[2] https://github.com/yskzalloc/kcov-dataflow
Fixes:
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