* Re: [PATCH] __check_pf: Add a cancellation cleanup handler [BZ #20975]
[not found] ` <CAFUsyfKE1o3G+G4q8BSfEGRDMiiMw3_RgLZZRnMzuyni-aFSjw@mail.gmail.com>
@ 2023-05-22 20:37 ` H.J. Lu
2023-05-23 8:58 ` Florian Weimer
0 siblings, 1 reply; 3+ messages in thread
From: H.J. Lu @ 2023-05-22 20:37 UTC (permalink / raw)
To: Noah Goldstein, Libc-stable Mailing List; +Cc: libc-alpha
On Fri, Apr 28, 2023 at 12:17 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Thu, Apr 27, 2023 at 3:06 PM H.J. Lu via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > There are reports for hang in __check_pf:
> >
> > https://github.com/JoeDog/siege/issues/4
> >
> > It is reproducible only under specific configurations:
> >
> > 1. Large number of cores (>= 64) and large number of threads (> 3X of
> > the number of cores) with long lived socket connection.
> > 2. Low power (frequency) mode.
> > 3. Power management is enabled.
> >
> > While holding lock, __check_pf calls make_request which calls __sendto
> > and __recvmsg. Since __sendto and __recvmsg are cancellation points,
> > lock held by __check_pf won't be released and can cause deadlock when
> > thread cancellation happens in __sendto or __recvmsg. Add a cancellation
> > cleanup handler for __check_pf to unlock the lock when cancelled by
> > another thread. This fixes BZ #20975 and the siege hang issue.
> > ---
> > sysdeps/unix/sysv/linux/Makefile | 2 ++
> > sysdeps/unix/sysv/linux/check_pf.c | 15 +++++++++++++++
> > 2 files changed, 17 insertions(+)
> >
> > diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> > index aec7a94785..0160be8790 100644
> > --- a/sysdeps/unix/sysv/linux/Makefile
> > +++ b/sysdeps/unix/sysv/linux/Makefile
> > @@ -529,6 +529,8 @@ sysdep_headers += \
> > sysdep_routines += \
> > netlink_assert_response \
> > # sysdep_routines
> > +
> > +CFLAGS-check_pf.c += -fexceptions
> > endif
> >
> > # Don't compile the ctype glue code, since there is no old non-GNU C library.
> > diff --git a/sysdeps/unix/sysv/linux/check_pf.c b/sysdeps/unix/sysv/linux/check_pf.c
> > index b157c5126c..2b0b8b6368 100644
> > --- a/sysdeps/unix/sysv/linux/check_pf.c
> > +++ b/sysdeps/unix/sysv/linux/check_pf.c
> > @@ -292,6 +292,14 @@ make_request (int fd, pid_t pid)
> > return NULL;
> > }
> >
> > +#ifdef __EXCEPTIONS
> > +static void
> > +cancel_handler (void *arg __attribute__((unused)))
> > +{
> > + /* Release the lock. */
> > + __libc_lock_unlock (lock);
> > +}
> > +#endif
> >
> > void
> > attribute_hidden
> > @@ -304,6 +312,10 @@ __check_pf (bool *seen_ipv4, bool *seen_ipv6,
> > struct cached_data *olddata = NULL;
> > struct cached_data *data = NULL;
> >
> > +#ifdef __EXCEPTIONS
> > + /* Make sure that lock is released when the thread is cancelled. */
> > + __libc_cleanup_push (cancel_handler, NULL);
> > +#endif
> > __libc_lock_lock (lock);
> >
> > if (cache_valid_p ())
> > @@ -338,6 +350,9 @@ __check_pf (bool *seen_ipv4, bool *seen_ipv6,
> > }
> > }
> >
> > +#ifdef __EXCEPTIONS
> > + __libc_cleanup_pop (0);
> > +#endif
> > __libc_lock_unlock (lock);
> >
> > if (data != NULL)
> > --
> > 2.40.0
> >
>
> LGTM.
OK for release branches?
Thanks.
--
H.J.
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