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();