On 2/23/22 19:48, Gaetan Rivet wrote:
> The ofproto map 'all_ofproto_dpifs_by_uuid' does not support
> concurrent accesses. It is however read by upcall handler threads
> and written by the main thread at the same time.
>
> Additionally, handler threads will change the ams_seq while
> an ofproto is being destroyed, triggering crashes with the
> following backtrace:
>
> (gdb) bt
> hmap_next (hmap.h:398)
> seq_wake_waiters (seq.c:326)
> seq_change_protected (seq.c:134)
> seq_change (seq.c:144)
> ofproto_dpif_send_async_msg (ofproto_dpif.c:263)
> process_upcall (ofproto_dpif_upcall.c:1782)
> recv_upcalls (ofproto_dpif_upcall.c:1026)
> udpif_upcall_handler (ofproto/ofproto_dpif_upcall.c:945)
> ovsthread_wrapper (ovs_thread.c:734)
>
> To solve both issues, remove the 'all_ofproto_dpifs_by_uuid'.
> Instead, another map already storing ofprotos in xlate can be used.
>
> During an ofproto destruction, its reference is removed from the current
> xlate xcfg. Such change is committed only after all threads have quiesced
> at least once during xlate_txn_commit(). This wait ensures that the
> removal is seen by all threads, rendering impossible for a thread to
> still hold a reference while the destruction proceeds.
>
> Furthermore, the xlate maps are copied during updates instead of
> being written in place. It is thus correct to read xcfg->xbridges while
> inserting or removing from new_xcfg->xbridges.
>
> Finally, now that ofproto_dpifs lookups are done through xcfg->xbridges,
> it is important to use a high level of entropy. As it used the ofproto pointer
> hashed, fewer bits were random compared to the uuid key used in
> 'all_ofproto_dpifs_by_uuid'. To solve this, use the ofproto uuid as the key
> in xbridges as well, improving entropy.
>
> Fixes: fcb9579be3c7 ("ofproto: Add 'ofproto_uuid' and 'ofp_in_port' to user
> action cookie.")
> Suggested-by: Adrian Moreno <[email protected]>
> Signed-off-by: Yunjian Wang <[email protected]>
> Signed-off-by: Gaetan Rivet <[email protected]>
> ---
Thanks, everyone! Applied and backported down to 2.13.
Best regards, Ilya Maximets.
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