svn commit: r329448 - head/sys/kern
Mateusz Guzik
mjguzik at gmail.com
Sat Feb 17 16:07:08 UTC 2018
On Sat, Feb 17, 2018 at 01:27:38PM +0200, Konstantin Belousov wrote:
> On Sat, Feb 17, 2018 at 08:48:46AM +0000, Mateusz Guzik wrote:
> > Author: mjg
> > Date: Sat Feb 17 08:48:45 2018
> > New Revision: 329448
> > URL: https://svnweb.freebsd.org/changeset/base/329448
> >
> > Log:
> > exit: get rid of PROC_SLOCK when checking a process to report
> Was this tested ?
>
I was trussing multithreaded microbenchmarks, no issues.
> In particular, are you aware of r309539 ?
>
So it looks like I misread the code - I have grepped
thread_suspend_switch operating with the proc locked and misread
thread_suspend_one's assert as PROC_LOCK_ASSERT.
That said, I think this is harmless. Regardless of the lock the
inspecting thread can race and check "too soon". Even for a case where
it decides to report, I don't see anything which would depend on the
suspending thread to finish.
However, locking can be employed in a way which is avoided in the common
case:
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index b063bda5b7ff..4ae24bcd7059 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -1174,6 +1174,7 @@ kern_wait6(struct thread *td, idtype_t idtype, id_t
id, int *status,
struct proc *p, *q;
pid_t pid;
int error, nfound, ret;
+ bool report;
AUDIT_ARG_VALUE((int)idtype); /* XXX - This is likely wrong! */
AUDIT_ARG_PID((pid_t)id); /* XXX - This may be wrong! */
@@ -1226,27 +1227,36 @@ kern_wait6(struct thread *td, idtype_t idtype, id_t
id, int *status,
PROC_LOCK_ASSERT(p, MA_OWNED);
if ((options & WTRAPPED) != 0 &&
- (p->p_flag & P_TRACED) != 0 &&
- (p->p_flag & (P_STOPPED_TRACE | P_STOPPED_SIG)) != 0 &&
- p->p_suspcount == p->p_numthreads &&
- (p->p_flag & P_WAITED) == 0) {
+ (p->p_flag & P_TRACED) != 0) {
+ PROC_SLOCK(p);
+ report =
+ ((p->p_flag & (P_STOPPED_TRACE |
P_STOPPED_SIG)) &&
+ p->p_suspcount == p->p_numthreads &&
+ (p->p_flag & P_WAITED) == 0);
+ PROC_SUNLOCK(p);
+ if (report) {
CTR4(KTR_PTRACE,
"wait: returning trapped pid %d status %#x "
"(xstat %d) xthread %d",
p->p_pid, W_STOPCODE(p->p_xsig), p->p_xsig,
p->p_xthread != NULL ?
p->p_xthread->td_tid : -1);
- report_alive_proc(td, p, siginfo, status, options,
- CLD_TRAPPED);
- return (0);
+ report_alive_proc(td, p, siginfo, status,
+ options, CLD_TRAPPED);
+ return (0);
+ }
}
if ((options & WUNTRACED) != 0 &&
- (p->p_flag & P_STOPPED_SIG) != 0 &&
- p->p_suspcount == p->p_numthreads &&
- (p->p_flag & P_WAITED) == 0) {
- report_alive_proc(td, p, siginfo, status, options,
+ report_alive_proc(td, p, siginfo, status,
+ options, CLD_TRAPPED);
+ return (0);
+ }
}
if ((options & WUNTRACED) != 0 &&
- (p->p_flag & P_STOPPED_SIG) != 0 &&
- p->p_suspcount == p->p_numthreads &&
- (p->p_flag & P_WAITED) == 0) {
- report_alive_proc(td, p, siginfo, status, options,
- CLD_STOPPED);
- return (0);
+ (p->p_flag & P_STOPPED_SIG) != 0) {
+ PROC_SLOCK(p);
+ report = (p->p_suspcount == p->p_numthreads &&
+ ((p->p_flag & P_WAITED) == 0));
+ PROC_SUNLOCK(p);
+ if (report) {
+ report_alive_proc(td, p, siginfo, status,
+ options, CLD_STOPPED);
+ return (0);
+ }
}
if ((options & WCONTINUED) != 0 &&
(p->p_flag & P_CONTINUED) != 0) {
On Sat, Feb 17, 2018 at 12:27 PM, Konstantin Belousov <kostikbel at gmail.com>
wrote:
> On Sat, Feb 17, 2018 at 08:48:46AM +0000, Mateusz Guzik wrote:
> > Author: mjg
> > Date: Sat Feb 17 08:48:45 2018
> > New Revision: 329448
> > URL: https://svnweb.freebsd.org/changeset/base/329448
> >
> > Log:
> > exit: get rid of PROC_SLOCK when checking a process to report
> Was this tested ?
>
> In particular, are you aware of r309539 ?
>
> >
> > All accessed fields are protected with already held process lock.
> >
> > Modified:
> > head/sys/kern/kern_exit.c
> >
> > Modified: head/sys/kern/kern_exit.c
> > ============================================================
> ==================
> > --- head/sys/kern/kern_exit.c Sat Feb 17 08:12:35 2018 (r329447)
> > +++ head/sys/kern/kern_exit.c Sat Feb 17 08:48:45 2018 (r329448)
> > @@ -1228,15 +1228,11 @@ loop_locked:
> > nfound++;
> > PROC_LOCK_ASSERT(p, MA_OWNED);
> >
> > - if ((options & (WTRAPPED | WUNTRACED)) != 0)
> > - PROC_SLOCK(p);
> > -
> > if ((options & WTRAPPED) != 0 &&
> > (p->p_flag & P_TRACED) != 0 &&
> > (p->p_flag & (P_STOPPED_TRACE | P_STOPPED_SIG)) != 0 &&
> > p->p_suspcount == p->p_numthreads &&
> > (p->p_flag & P_WAITED) == 0) {
> > - PROC_SUNLOCK(p);
> > CTR4(KTR_PTRACE,
> > "wait: returning trapped pid %d status %#x "
> > "(xstat %d) xthread %d",
> > @@ -1251,13 +1247,10 @@ loop_locked:
> > (p->p_flag & P_STOPPED_SIG) != 0 &&
> > p->p_suspcount == p->p_numthreads &&
> > (p->p_flag & P_WAITED) == 0) {
> > - PROC_SUNLOCK(p);
> > report_alive_proc(td, p, siginfo, status, options,
> > CLD_STOPPED);
> > return (0);
> > }
> > - if ((options & (WTRAPPED | WUNTRACED)) != 0)
> > - PROC_SUNLOCK(p);
> > if ((options & WCONTINUED) != 0 &&
> > (p->p_flag & P_CONTINUED) != 0) {
> > report_alive_proc(td, p, siginfo, status, options,
>
--
Mateusz Guzik <mjguzik gmail.com>
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