Date: Thu, 19 Mar 2015 19:35:30 +0800 From: Tiwei Bie <btw@mail.ustc.edu.cn> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-hackers@freebsd.org, mjguzik@gmail.com Subject: Re: [PATCH] Finish the task 'Fix corefilename race' Message-ID: <20150319113530.GA33176@freebsd> In-Reply-To: <20150319101019.GZ2379@kib.kiev.ua> References: <1426749223-18118-1-git-send-email-btw@mail.ustc.edu.cn> <20150319101019.GZ2379@kib.kiev.ua>
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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.
Here is my new patch:
---
sys/kern/kern_sig.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 58d9707..cc99f8f 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -3089,9 +3089,24 @@ SYSCTL_INT(_kern, OID_AUTO, compress_user_cores_gzlevel, CTLFLAG_RWTUN,
static int compress_user_cores = 0;
#endif
+#define corefilename_lock allprison_lock
+
static char corefilename[MAXPATHLEN] = {"%N.core"};
-SYSCTL_STRING(_kern, OID_AUTO, corefile, CTLFLAG_RWTUN, corefilename,
- sizeof(corefilename), "Process corefile name format string");
+
+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 +3135,7 @@ 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 +3178,7 @@ 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);
--
2.1.2
Best regards,
Tiwei Bie
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