Date: Thu, 19 Mar 2015 16:40:04 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Tiwei Bie <btw@mail.ustc.edu.cn> Cc: freebsd-hackers@freebsd.org, mjguzik@gmail.com Subject: Re: [PATCH] Finish the task 'Fix corefilename race' Message-ID: <20150319144004.GD2379@kib.kiev.ua> In-Reply-To: <20150319113530.GA33176@freebsd> References: <1426749223-18118-1-git-send-email-btw@mail.ustc.edu.cn> <20150319101019.GZ2379@kib.kiev.ua> <20150319113530.GA33176@freebsd>
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On Thu, Mar 19, 2015 at 07:35:30PM +0800, Tiwei Bie wrote:
> On Thu, Mar 19, 2015 at 12:10:19PM +0200, Konstantin Belousov wrote:
> > On Thu, Mar 19, 2015 at 03:13:43PM +0800, Tiwei Bie wrote:
> > > Hi, Mateusz!
> > >
> > > I have finished the task: Fix corefilename race [1].
> > >
> > > Following is my patch:
> > >
> > > ---
> > > sys/kern/kern_sig.c | 22 ++++++++++++++++++++--
> > > 1 file changed, 20 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
> > > index 58d9707..a1421cb 100644
> > > --- a/sys/kern/kern_sig.c
> > > +++ b/sys/kern/kern_sig.c
> > > @@ -3090,8 +3090,24 @@ static int compress_user_cores = 0;
> > > #endif
> > >
> > > static char corefilename[MAXPATHLEN] = {"%N.core"};
> > > -SYSCTL_STRING(_kern, OID_AUTO, corefile, CTLFLAG_RWTUN, corefilename,
> > > - sizeof(corefilename), "Process corefile name format string");
> > > +
> > > +static struct sx corefilename_lock;
> > > +SX_SYSINIT(corefilename_init, &corefilename_lock, "corefilename lock");
> > > +
> > > +static int
> > > +sysctl_kern_corefile(SYSCTL_HANDLER_ARGS)
> > > +{
> > > + int error;
> > > +
> > > + sx_xlock(&corefilename_lock);
> > > + error = sysctl_handle_string(oidp, corefilename, MAXPATHLEN, req);
> > > + sx_xunlock(&corefilename_lock);
> > > +
> > > + return (error);
> > > +}
> > > +SYSCTL_PROC(_kern, OID_AUTO, corefile, CTLTYPE_STRING | CTLFLAG_RWTUN |
> > > + CTLFLAG_MPSAFE, 0, 0, sysctl_kern_corefile, "A",
> > > + "Process corefile name format string");
> > >
> > > /*
> > > * corefile_open(comm, uid, pid, td, compress, vpp, namep)
> > > @@ -3120,6 +3136,7 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td,
> > > name = malloc(MAXPATHLEN, M_TEMP, M_WAITOK | M_ZERO);
> > > indexpos = -1;
> > > (void)sbuf_new(&sb, name, MAXPATHLEN, SBUF_FIXEDLEN);
> > > + sx_slock(&corefilename_lock);
> > > for (i = 0; format[i] != '\0'; i++) {
> > > switch (format[i]) {
> > > case '%': /* Format character */
> > > @@ -3162,6 +3179,7 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td,
> > > break;
> > > }
> > > }
> > > + sx_sunlock(&corefilename_lock);
> > > free(hostname, M_TEMP);
> > > if (compress)
> > > sbuf_printf(&sb, GZ_SUFFIX);
> >
> > So the race is between somebody setting the core path string and another
> > process coredumping, am I right ?
> >
>
> Yeah, you are right!
>
> > If you, could you try to reuse some existing lock for the task ? It is a
> > waste to have sx dedicated to the task, which is probably never used by
> > 99% of the machines in the world.
>
> Yeah, of course. After a quick `grep'ing, I found the sx lock: allprison_lock,
> which is defined in kern/kern_jail.c. It is rarely acquired as an exclusive
> lock, and is not defined as a static variable. So I think it will be a good
> candidate for this task.
I think it is too quick grepping. allprison_lock is completely unrelated
to the process management. Please consider to utilize some lock used
for the process management.
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