2.6.36-stable review patch. If anyone has any objections, please let us know.
------------------ From: Thomas Gleixner <[email protected]> commit dddd3379a619a4cb8247bfd3c94ca9ae3797aa2e upstream. It was found that sometimes children of tasks with inherited events had one extra event. Eventually it turned out to be due to the list rotation no being exclusive with the list iteration in the inheritance code. Cure this by temporarily disabling the rotation while we inherit the events. Signed-off-by: Thomas Gleixner <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- include/linux/perf_event.h | 1 + kernel/perf_event.c | 22 ++++++++++++++++++++-- 2 files changed, 21 insertions(+), 2 deletions(-) --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -788,6 +788,7 @@ struct perf_event_context { int nr_active; int is_active; int nr_stat; + int rotate_disable; atomic_t refcount; struct task_struct *task; --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -1620,8 +1620,12 @@ static void rotate_ctx(struct perf_event { raw_spin_lock(&ctx->lock); - /* Rotate the first entry last of non-pinned groups */ - list_rotate_left(&ctx->flexible_groups); + /* + * Rotate the first entry last of non-pinned groups. Rotation might be + * disabled by the inheritance code. + */ + if (!ctx->rotate_disable) + list_rotate_left(&ctx->flexible_groups); raw_spin_unlock(&ctx->lock); } @@ -5622,6 +5626,7 @@ int perf_event_init_task(struct task_str struct perf_event *event; struct task_struct *parent = current; int inherited_all = 1; + unsigned long flags; int ret = 0; child->perf_event_ctxp = NULL; @@ -5662,6 +5667,15 @@ int perf_event_init_task(struct task_str break; } + /* + * We can't hold ctx->lock when iterating the ->flexible_group list due + * to allocations, but we need to prevent rotation because + * rotate_ctx() will change the list from interrupt context. + */ + raw_spin_lock_irqsave(&parent_ctx->lock, flags); + parent_ctx->rotate_disable = 1; + raw_spin_unlock_irqrestore(&parent_ctx->lock, flags); + list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) { ret = inherit_task_group(event, parent, parent_ctx, child, &inherited_all); @@ -5669,6 +5683,10 @@ int perf_event_init_task(struct task_str break; } + raw_spin_lock_irqsave(&parent_ctx->lock, flags); + parent_ctx->rotate_disable = 0; + raw_spin_unlock_irqrestore(&parent_ctx->lock, flags); + child_ctx = child->perf_event_ctxp; if (child_ctx && inherited_all) { _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
