Hi Al,
I totally agree the Greg's suggestion, I think v9fs is the direction
as the VirtFS in the virtualization field, that it still deserves to
be used and developed, so I also suggestion you can apply (or nack)
the patch as v9fs maintainer, I hope you won't refuse.
Thanks,
Yiwen.
On 2018/2/21 0:48, Greg Kurz wrote:
> Hi Al,
>
> It's been two years without any sign of life from 9p maintainers... :-\
>
> Would you apply (or nack) this patch ?
>
> Thanks,
>
> --
> Greg
>
> PS: in the case you apply it, probable Cc sta...@vger.kernel.org as well
>
>
> On Thu, 08 Feb 2018 18:38:49 +0100
>
> Greg Kurz <gr...@kaod.org> wrote:
>
>> If it was interrupted by a signal, the 9p client may need to send some
>> more requests to the server for cleanup before returning to userspace.
>>
>> To avoid such a last minute request to be interrupted right away, the
>> client memorizes if a signal is pending, clear TIF_SIGPENDING, handle
>> the request and call recalc_sigpending() before returning.
>>
>> Unfortunately, if the transmission of this cleanup request fails for any
>> reason, the transport returns an error and the client propagates it right
>> away, without calling recalc_sigpending().
>>
>> This ends up with -ERESTARTSYS from the initially interrupted request
>> crawling up to syscall exit, with TIF_SIGPENDING cleared by the cleanup
>> request. The specific signal handling code, which is responsible for
>> converting -ERESTARTSYS to -EINTR is not called, and userspace receives
>> the confusing errno value:
>>
>> open: Unknown error 512 (512)
>>
>> This is really hard to hit in real life. I discovered the issue while
>> working on hot-unplug of a virtio-9p-pci device with an instrumented
>> QEMU allowing to control request completion.
>>
>> Both p9_client_zc_rpc() and p9_client_rpc() functions have this buggy
>> error path actually. Their code flow is a bit obscure and the best
>> thing to do would probably be a full rewrite: to really ensure this
>> situation of clearing TIF_SIGPENDING and returning -ERESTARTSYS can
>> never happen.
>>
>> But given the general lack of interest for the 9p code, I won't risk
>> breaking more things. So this patch simply fix the buggy paths in both
>> functions with a trivial label+goto.
>>
>> Thanks to Laurent Dufour for his help and suggestions on how to find
>> the root cause and how to fix it.
>>
>> Signed-off-by: Greg Kurz <gr...@kaod.org>
>> ---
>> net/9p/client.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/9p/client.c b/net/9p/client.c
>> index 4c8cf9c1631a..5154eaf19fff 100644
>> --- a/net/9p/client.c
>> +++ b/net/9p/client.c
>> @@ -769,7 +769,7 @@ p9_client_rpc(struct p9_client *c, int8_t type, const
>> char *fmt, ...)
>> if (err < 0) {
>> if (err != -ERESTARTSYS && err != -EFAULT)
>> c->status = Disconnected;
>> - goto reterr;
>> + goto recalc_sigpending;
>> }
>> again:
>> /* Wait for the response */
>> @@ -804,6 +804,7 @@ p9_client_rpc(struct p9_client *c, int8_t type, const
>> char *fmt, ...)
>> if (req->status == REQ_STATUS_RCVD)
>> err = 0;
>> }
>> +recalc_sigpending:
>> if (sigpending) {
>> spin_lock_irqsave(¤t->sighand->siglock, flags);
>> recalc_sigpending();
>> @@ -867,7 +868,7 @@ static struct p9_req_t *p9_client_zc_rpc(struct
>> p9_client *c, int8_t type,
>> if (err == -EIO)
>> c->status = Disconnected;
>> if (err != -ERESTARTSYS)
>> - goto reterr;
>> + goto recalc_sigpending;
>> }
>> if (req->status == REQ_STATUS_ERROR) {
>> p9_debug(P9_DEBUG_ERROR, "req_status error %d\n", req->t_err);
>> @@ -885,6 +886,7 @@ static struct p9_req_t *p9_client_zc_rpc(struct
>> p9_client *c, int8_t type,
>> if (req->status == REQ_STATUS_RCVD)
>> err = 0;
>> }
>> +recalc_sigpending:
>> if (sigpending) {
>> spin_lock_irqsave(¤t->sighand->siglock, flags);
>> recalc_sigpending();
>>
>>
>> ------------------------------------------------------------------------------
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>
>
> ------------------------------------------------------------------------------
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> https://lists.sourceforge.net/lists/listinfo/v9fs-developer
>
> .
>
