Re: [Qemu-devel] [PATCH RFC v3 1/7] Fix segmentation fault when qemu_signal_init fails

[Fei Li]

On 09/19/2018 10:49 PM, Fam Zheng wrote:
> On Wed, 09/19 21:35, Fei Li wrote:
> > Currently, when qemu_signal_init() fails it only returns a non-zero
> > value but without propagating any Error. But its callers need a
> > non-null err when runs error_report_err(err), or else 0->msg occurs.
> >
> > To avoid such segmentation fault, add a new Error parameter to make
> > the call trace to propagate the err to the final caller.
> >
> > This patch also adds the omitted error handling when creating signalfd
> > pipe fails in qemu_signalfd_compat().
> >
> > Signed-off-by: Fei Li <address@hidden>
> > ---
> >   include/qemu/osdep.h |  2 +-
> >   util/compatfd.c      |  9 ++++++---
> >   util/main-loop.c     | 11 +++++------
> >   3 files changed, 12 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index a91068df0e..09ed85fcb8 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -421,7 +421,7 @@ struct qemu_signalfd_siginfo {
> >                                additional fields in the future) */
> >   };
> >   
> > -int qemu_signalfd(const sigset_t *mask);
> > +int qemu_signalfd(const sigset_t *mask, Error **errp);
> >   void sigaction_invoke(struct sigaction *action,
> >                         struct qemu_signalfd_siginfo *info);
> >   #endif
> > diff --git a/util/compatfd.c b/util/compatfd.c
> > index 980bd33e52..d3ed890405 100644
> > --- a/util/compatfd.c
> > +++ b/util/compatfd.c
> > @@ -16,6 +16,7 @@
> >   #include "qemu/osdep.h"
> >   #include "qemu-common.h"
> >   #include "qemu/thread.h"
> > +#include "qapi/error.h"
> >   
> >   #include <sys/syscall.h>
> >   
> > @@ -65,7 +66,7 @@ static void *sigwait_compat(void *opaque)
> >       }
> >   }
> >   
> > -static int qemu_signalfd_compat(const sigset_t *mask)
> > +static int qemu_signalfd_compat(const sigset_t *mask, Error **errp)
> >   {
> >       struct sigfd_compat_info *info;
> >       QemuThread thread;
> > @@ -73,11 +74,13 @@ static int qemu_signalfd_compat(const sigset_t *mask)
> >   
> >       info = malloc(sizeof(*info));
> >       if (info == NULL) {
> > +        error_setg(errp, "Failed to allocate signalfd memory");
> >           errno = ENOMEM;
> >           return -1;
> >       }
> >   
> >       if (pipe(fds) == -1) {
> > +        error_setg(errp, "Failed to create signalfd pipe");
> >           free(info);
> >           return -1;
> >       }
> > @@ -94,7 +97,7 @@ static int qemu_signalfd_compat(const sigset_t *mask)
> >       return fds[0];
> >   }
> >   
> > -int qemu_signalfd(const sigset_t *mask)
> > +int qemu_signalfd(const sigset_t *mask, Error **errp)
> >   {
> >   #if defined(CONFIG_SIGNALFD)
> >       int ret;
> > @@ -106,5 +109,5 @@ int qemu_signalfd(const sigset_t *mask)
> >       }
> >   #endif
> >   
> > -    return qemu_signalfd_compat(mask);
> > +    return qemu_signalfd_compat(mask, errp);
> >   }
> > diff --git a/util/main-loop.c b/util/main-loop.c
> > index affe0403c5..b783f3c806 100644
> > --- a/util/main-loop.c
> > +++ b/util/main-loop.c
> > @@ -71,7 +71,7 @@ static void sigfd_handler(void *opaque)
> >       }
> >   }
> >   
> > -static int qemu_signal_init(void)
> > +static int qemu_signal_init(Error **errp)
> >   {
> >       int sigfd;
> >       sigset_t set;
> > @@ -94,10 +94,9 @@ static int qemu_signal_init(void)
> >       pthread_sigmask(SIG_BLOCK, &set, NULL);
> >   
> >       sigdelset(&set, SIG_IPI);
> > -    sigfd = qemu_signalfd(&set);
> > +    sigfd = qemu_signalfd(&set, errp);
> >       if (sigfd == -1) {
> > -        fprintf(stderr, "failed to create signalfd\n");
> > -        return -errno;
> > +        return -1;
> Why change from -errno to -1?
I changed this for two reasons.
One is I misunderstood that if pipe() fails the errno is not set 
automatically.
And that's why I wrote the third paragraph in the commit message. Obviously
what I thought was wrong, and I will delete that msg in next version. :)
The second is for the following qemu_thread_create(), the current code 
returns
a boolean true/false instead of the int err, considering propagating the 
error
message and returning a int err may be duplicated.

But considering "return -errno" explains the failure reason and my 
misunderstood
about pipe(), I'd prefer using "return -errno;" and adding the 
"errno=err" in the
qemu_thread_create() function in patch 7/7. What do you think?

Have a nice day, thanks
Fei
> >       }
> >   
> >       fcntl_setfl(sigfd, O_NONBLOCK);
> > @@ -109,7 +108,7 @@ static int qemu_signal_init(void)
> >   
> >   #else /* _WIN32 */
> >   
> > -static int qemu_signal_init(void)
> > +static int qemu_signal_init(Error **errp)
> >   {
> >       return 0;
> >   }
> > @@ -148,7 +147,7 @@ int qemu_init_main_loop(Error **errp)
> >   
> >       init_clocks(qemu_timer_notify_cb);
> >   
> > -    ret = qemu_signal_init();
> > +    ret = qemu_signal_init(errp);
> >       if (ret) {
> >           return ret;
> >       }
> > --
> > 2.13.7