Hello.
Amit S. Kale wrote:
This thread came up on kgdb-bugreport mailing list. Could you please suggest
us what's the correct way of fixing this problem?
1. When running a kgdb on RTL8139 ethernet interface: 8139too driver prints
too many "Out-of-sync dirty pointer" messages on console and gdb can't
connect to kgdb stub. These messages can be suppressed, though it still
results in connection failures frequently.
2. Here is how kgdb uses polling mechanism for communication to gdb. kgdb
calls netpoll_set_trap(1) just before entering a loop where it communicates
to gdb. It calls netpoll_set_trap(0) after it is done and wants to resume a
kernel. The communication to gdb goes through netpoll_poll (which calls kgdb
rx_hook) and netpoll_send_udp functions.
3. A queue for an interface may have been stopped by it's driver by calling
netif_stop_queue. After this if kgdb attempts to enter communication with
gdb, it'll call netpoll_set_trap(1), after which the queue can't be started
again. This is a potential deadlock situation. Is there a way out of this?
4. Is it necessary to call netpoll_set_trap(1) at all before entering gdb
communication loop? Even if a driver stops the queue in middle of the
communication netpoll_poll and netpoll_send_udp calls can recover from that
by calling driver's interrupt and poll routines. Is this a valid statement?
I'd like to return to this again (having received no feedback)...
The idea is to change how CONFIG_NETPOLL_TRAP is implemented: instead of
completely bypassing queue locking after netpoll_set_trap(1) has been called,
how about we set and chack some other flag (internal to netpoll) telling it
that the queue is frozen, i.e. watch the queue state using a separate
mechanism when traffic trapping is engaged? This certainly would avoid TX
queue overflows in drivers while also avoiding any dev->state changes and even
worse evil __netif_schedule() call, i.e. things that CONFIG_NETPOLL_TRAP is
currectly trying to avoid, AFAIU...
Thanks a lot.
-Amit
WBR, Sergei
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