lkml.org 
[lkml]   [2015]   [Sep]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[RFC][PATCH 1/3] perf: Restructure perf syscall point of no return
The exclusive_event_installable() stuff only works because its
exclusive with the grouping bits.

Rework the code such that there is a sane place to error out before we
go do things we cannot undo.

Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/events/core.c | 108 ++++++++++++++++++++++++++++++++++++---------------
1 file changed, 78 insertions(+), 30 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8242,15 +8271,31 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_context;
}

- if (move_group) {
- gctx = group_leader->ctx;
+ gctx = group_leader->ctx;
+ if (move_group)
+ mutex_lock_double(&gctx->mutex, &ctx->mutex);
+ else
+ mutex_lock(&ctx->mutex);

+ /*
+ * Must be under the same ctx::mutex as perf_install_in_context(),
+ * because we need to serialize with concurrent event creation.
+ */
+ if (!exclusive_event_installable(event, ctx)) {
+ /* exclusive and group stuff are assumed mutually exclusive */
+ WARN_ON_ONCE(move_group);
+
+ err = -EBUSY;
+ goto err_locked;
+ }
+
+ WARN_ON_ONCE(ctx->parent_ctx);
+
+ if (move_group) {
/*
* See perf_event_ctx_lock() for comments on the details
* of swizzling perf_event::ctx.
*/
- mutex_lock_double(&gctx->mutex, &ctx->mutex);
-
perf_remove_from_context(group_leader, false);

list_for_each_entry(sibling, &group_leader->sibling_list,
@@ -8258,13 +8308,7 @@ SYSCALL_DEFINE5(perf_event_open,
perf_remove_from_context(sibling, false);
put_ctx(gctx);
}
- } else {
- mutex_lock(&ctx->mutex);
- }

- WARN_ON_ONCE(ctx->parent_ctx);
-
- if (move_group) {
/*
* Wait for everybody to stop referencing the events through
* the old lists, before installing it on new lists.
@@ -8296,22 +8340,20 @@ SYSCALL_DEFINE5(perf_event_open,
perf_event__state_init(group_leader);
perf_install_in_context(ctx, group_leader, group_leader->cpu);
get_ctx(ctx);
- }

- if (!exclusive_event_installable(event, ctx)) {
- err = -EBUSY;
- mutex_unlock(&ctx->mutex);
- fput(event_file);
- goto err_context;
+ /*
+ * Now that all events are installed in @ctx, nothing
+ * references @gctx anymore, so drop the last reference we have
+ * on it.
+ */
+ put_ctx(gctx);
}

perf_install_in_context(ctx, event, event->cpu);
perf_unpin_context(ctx);

- if (move_group) {
+ if (move_group)
mutex_unlock(&gctx->mutex);
- put_ctx(gctx);
- }
mutex_unlock(&ctx->mutex);

put_online_cpus();
@@ -8338,6 +8380,12 @@ SYSCALL_DEFINE5(perf_event_open,
fd_install(event_fd, event_file);
return event_fd;

+err_locked:
+ if (move_group)
+ mutex_unlock(&gctx->mutex);
+ mutex_unlock(&ctx->mutex);
+/* err_file: */
+ fput(event_file);
err_context:
perf_unpin_context(ctx);
put_ctx(ctx);



\
 
 \ /
  Last update: 2015-09-10 18:41    [W:0.130 / U:1.688 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site