Re: [PATCH] IPoIB: Fix race in deleting ipoib_neigh entries

[Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 09/08/2013 03:44, Jim Foraker wrote:
> 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-i2BcT+NCU+M@public.gmane.org>

Hi Jim,

I have reviewed the patch with Shlomo who did the neighboring changes in 
IPoIB -- impressive analysis and debugging, a good and proper fix to the 
issue presented e.g here marc.info/?l=linux-rdma&m=136881939301117&w=2


Or.


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