From: Pedro Alves Date: Sun, 15 Mar 2015 19:35:26 +0000 (+0000) Subject: gdbserver/Linux: unbreak thread event randomization X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=8bf3b159e55b42bb084f9da1af400a285025618f;p=binutils-gdb.git gdbserver/Linux: unbreak thread event randomization Wanting to make sure the new continue-pending-status.exp test tests both cases of threads 2 and 3 reporting an event, I added counters to the test, to make it FAIL if events for both threads aren't seen. Assuming a well behaved backend, and given a reasonable number of iterations, it should PASS. However, running that against GNU/Linux gdbserver, I found that surprisingly, that FAILed. GDBserver always reported the breakpoint hit for the same thread. Turns out that I broke gdbserver's thread event randomization recently, with git commit 582511be ([gdbserver] linux-low.c: better starvation avoidance, handle non-stop mode too). In that commit I missed that the thread structure also has a status_pending_p field... The end result was that count_events_callback always returns 0, and then if no thread is stepping, select_event_lwp always returns the event thread. IOW, no randomization is happening at all. Quite curious how all the other changes in that patch were sufficient to fix non-stop-fair-events.exp anyway even with that broken. Tested on x86_64 Fedora 20, native and gdbserver. gdb/gdbserver/ChangeLog: 2015-03-19 Pedro Alves * linux-low.c (count_events_callback, select_event_lwp_callback): Use the lwp's status_pending_p field, not the thread's. gdb/testsuite/ChangeLog: 2015-03-19 Pedro Alves * gdb.threads/continue-pending-status.exp (saw_thread_2) (saw_thread_3): New globals. (top level): Increment them when an event for the corresponding thread is seen. (no thread starvation): New test. --- diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 7ae3c583477..cfbd576d5b8 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2015-03-19 Pedro Alves + + * linux-low.c (count_events_callback, select_event_lwp_callback): + Use the lwp's status_pending_p field, not the thread's. + 2015-03-19 Pedro Alves * linux-nat.c (status_callback): Return early if the LWP has no diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 6efab5b53d1..df8f9ab888c 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,8 @@ +2015-03-19 Pedro Alves + + * linux-low.c (count_events_callback, select_event_lwp_callback): + Use the lwp's status_pending_p field, not the thread's. + 2015-03-19 Pedro Alves * linux-low.c (select_event_lwp_callback): Update comments to diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c index 9558f463716..e53e0fc187d 100644 --- a/gdb/gdbserver/linux-low.c +++ b/gdb/gdbserver/linux-low.c @@ -2238,6 +2238,7 @@ static int count_events_callback (struct inferior_list_entry *entry, void *data) { struct thread_info *thread = (struct thread_info *) entry; + struct lwp_info *lp = get_thread_lwp (thread); int *count = data; gdb_assert (count != NULL); @@ -2245,7 +2246,7 @@ count_events_callback (struct inferior_list_entry *entry, void *data) /* Count only resumed LWPs that have an event pending. */ if (thread->last_status.kind == TARGET_WAITKIND_IGNORE && thread->last_resume_kind != resume_stop - && thread->status_pending_p) + && lp->status_pending_p) (*count)++; return 0; @@ -2273,6 +2274,7 @@ static int select_event_lwp_callback (struct inferior_list_entry *entry, void *data) { struct thread_info *thread = (struct thread_info *) entry; + struct lwp_info *lp = get_thread_lwp (thread); int *selector = data; gdb_assert (selector != NULL); @@ -2280,7 +2282,7 @@ select_event_lwp_callback (struct inferior_list_entry *entry, void *data) /* Select only resumed LWPs that have an event pending. */ if (thread->last_resume_kind != resume_stop && thread->last_status.kind == TARGET_WAITKIND_IGNORE - && thread->status_pending_p) + && lp->status_pending_p) if ((*selector)-- == 0) return 1; @@ -2324,6 +2326,7 @@ select_event_lwp (struct lwp_info **orig_lp) /* First see how many events we have. */ find_inferior (&all_threads, count_events_callback, &num_events); + gdb_assert (num_events > 0); /* Now randomly pick a LWP out of those that have had events. */ diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c index f5f92d9d96b..40f1e1fce40 100644 --- a/gdb/linux-nat.c +++ b/gdb/linux-nat.c @@ -2841,6 +2841,7 @@ select_event_lwp (ptid_t filter, struct lwp_info **orig_lp, int *status) /* First see how many events we have. */ iterate_over_lwps (filter, count_events_callback, &num_events); + gdb_assert (num_events > 0); /* Now randomly pick a LWP out of those that have had events. */ diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 94dae82fe98..6bf008a3df4 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,11 @@ +2015-03-19 Pedro Alves + + * gdb.threads/continue-pending-status.exp (saw_thread_2) + (saw_thread_3): New globals. + (top level): Increment them when an event for the corresponding + thread is seen. + (no thread starvation): New test. + 2015-03-19 Pedro Alves * gdb.threads/continue-pending-status.c: New file. diff --git a/gdb/testsuite/gdb.threads/continue-pending-status.exp b/gdb/testsuite/gdb.threads/continue-pending-status.exp index ff73ce4abbb..1f170f74ef4 100644 --- a/gdb/testsuite/gdb.threads/continue-pending-status.exp +++ b/gdb/testsuite/gdb.threads/continue-pending-status.exp @@ -56,6 +56,13 @@ proc get_current_thread {} { set attempts 20 +# These track whether we saw events for both threads 2 and 3. If the +# backend always returns the breakpoint hit for the same thread, then +# it fails to make sure threads aren't starved, and we'll fail the +# assert after the loop. +set saw_thread_2 0 +set saw_thread_3 0 + for {set i 0} {$i < $attempts} {incr i} { with_test_prefix "attempt $i" { gdb_test "b $srcfile:$break_line" \ @@ -71,8 +78,10 @@ for {set i 0} {$i < $attempts} {incr i} { # the resume and go straight to consuming the pending event. set thread [get_current_thread] if {$thread == 2} { + incr saw_thread_2 set thread 3 } else { + incr saw_thread_3 set thread 2 } gdb_test "thread $thread" \ @@ -108,3 +117,8 @@ for {set i 0} {$i < $attempts} {incr i} { } } } + +verbose -log "saw_thread_2=$saw_thread_2" +verbose -log "saw_thread_3=$saw_thread_3" + +gdb_assert {$saw_thread_2 > 0 && $saw_thread_3 > 0} "no thread starvation"