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 <[email protected]>
---
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();
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 [email protected] as well
On Thu, 08 Feb 2018 18:38:49 +0100
Greg Kurz <[email protected]> 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 <[email protected]>
> ---
> 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();
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> V9fs-developer mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/v9fs-developer
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 [email protected] as well
>
>
> On Thu, 08 Feb 2018 18:38:49 +0100
>
> Greg Kurz <[email protected]> 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 <[email protected]>
>> ---
>> 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();
>>
>>
>> ------------------------------------------------------------------------------
>> Check out the vibrant tech community on one of the world's most
>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>> _______________________________________________
>> V9fs-developer mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/v9fs-developer
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> V9fs-developer mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/v9fs-developer
>
> .
>