In several places, this snippet is used when removing neigh entries:
list_del(&neigh->list);
ipoib_neigh_free(neigh);
The list_del() removes neigh from the associated struct ipoib_path, while
ipoib_neigh_free() removes neigh from the device's neigh entry lookup
table. Both of these operations are protected by the priv->lock
spinlock. The table however is also protected via RCU, and so naturally
the lock is not held when doing reads.
This leads to a race condition, in which a thread may successfully look
up a neigh entry that has already been deleted from neigh->list. Since
the previous deletion will have marked the entry with poison, a second
list_del() on the object will cause a panic:
#5 [ffff8802338c3c70] general_protection at ffffffff815108c5
[exception RIP: list_del+16]
RIP: ffffffff81289020 RSP: ffff8802338c3d20 RFLAGS: 00010082
RAX: dead000000200200 RBX: ffff880433e60c88 RCX: 0000000000009e6c
RDX: 0000000000000246 RSI: ffff8806012ca298 RDI: ffff880433e60c88
RBP: ffff8802338c3d30 R8: ffff8806012ca2e8 R9: 00000000ffffffff
R10: 0000000000000001 R11: 0000000000000000 R12: ffff8804346b2020
R13: ffff88032a3e7540 R14: ffff8804346b26e0 R15: 0000000000000246
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0000
#6 [ffff8802338c3d38] ipoib_cm_tx_handler at ffffffffa066fe0a [ib_ipoib]
#7 [ffff8802338c3d98] cm_process_work at ffffffffa05149a7 [ib_cm]
#8 [ffff8802338c3de8] cm_work_handler at ffffffffa05161aa [ib_cm]
#9 [ffff8802338c3e38] worker_thread at ffffffff81090e10
#10 [ffff8802338c3ee8] kthread at ffffffff81096c66
#11 [ffff8802338c3f48] kernel_thread at ffffffff8100c0ca
We move the list_del() into ipoib_neigh_free(), so that deletion happens
only once, after the entry has been successfully removed from the lookup
table. This same behavior is already used in ipoib_del_neighs_by_gid()
and __ipoib_reap_neigh().
Signed-off-by: Jim Foraker <foraker1@llnl.gov>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Jack Wang <jinpu.wang@profitbricks.com>
Reviewed-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
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