From: Paul Mackerras Impact: better error reporting At present, if hw_perf_counter_init encounters an error, all it can do is return NULL, which causes sys_perf_counter_open to return an EINVAL error to userspace. This isn't very informative for userspace; it means that userspace can't tell the difference between "sorry, oprofile is already using the PMU" and "we don't support this CPU" and "this CPU doesn't support the requested generic hardware event". This commit uses the PTR_ERR/ERR_PTR/IS_ERR set of macros to let hw_perf_counter_init return an error code on error rather than just NULL if it wishes. If it does so, that error code will be returned from sys_perf_counter_open to userspace. If it returns NULL, an EINVAL error will be returned to userspace, as before. This also adapts the powerpc hw_perf_counter_init to make use of this to return ENXIO, EINVAL, EBUSY, or EOPNOTSUPP as appropriate. It would be good to add extra error numbers in future to allow userspace to distinguish the various errors that are currently reported as EINVAL, i.e. irq_period < 0, too many events in a group, conflict between exclude_* settings in a group, and PMU resource conflict in a group. [v2: fix a bug pointed out by Corey Ashford where error returns from hw_perf_counter_init were not handled correctly in the case of raw hardware events.] Signed-off-by: Paul Mackerras Signed-off-by: Peter Zijlstra --- arch/powerpc/kernel/perf_counter.c | 14 +++++++------- kernel/perf_counter.c | 35 ++++++++++++++++++++++------------- 2 files changed, 29 insertions(+), 20 deletions(-) Index: linux-2.6/arch/powerpc/kernel/perf_counter.c =================================================================== --- linux-2.6.orig/arch/powerpc/kernel/perf_counter.c +++ linux-2.6/arch/powerpc/kernel/perf_counter.c @@ -624,13 +624,13 @@ hw_perf_counter_init(struct perf_counter int err; if (!ppmu) - return NULL; + return ERR_PTR(-ENXIO); if ((s64)counter->hw_event.irq_period < 0) - return NULL; + return ERR_PTR(-EINVAL); if (!perf_event_raw(&counter->hw_event)) { ev = perf_event_id(&counter->hw_event); if (ev >= ppmu->n_generic || ppmu->generic_events[ev] == 0) - return NULL; + return ERR_PTR(-EOPNOTSUPP); ev = ppmu->generic_events[ev]; } else { ev = perf_event_config(&counter->hw_event); @@ -656,14 +656,14 @@ hw_perf_counter_init(struct perf_counter n = collect_events(counter->group_leader, ppmu->n_counter - 1, ctrs, events); if (n < 0) - return NULL; + return ERR_PTR(-EINVAL); } events[n] = ev; ctrs[n] = counter; if (check_excludes(ctrs, n, 1)) - return NULL; + return ERR_PTR(-EINVAL); if (power_check_constraints(events, n + 1)) - return NULL; + return ERR_PTR(-EINVAL); counter->hw.config = events[n]; atomic64_set(&counter->hw.period_left, counter->hw_event.irq_period); @@ -687,7 +687,7 @@ hw_perf_counter_init(struct perf_counter counter->destroy = hw_perf_counter_destroy; if (err) - return NULL; + return ERR_PTR(err); return &power_perf_ops; } Index: linux-2.6/kernel/perf_counter.c =================================================================== --- linux-2.6.orig/kernel/perf_counter.c +++ linux-2.6/kernel/perf_counter.c @@ -2453,10 +2453,11 @@ perf_counter_alloc(struct perf_counter_h { const struct hw_perf_counter_ops *hw_ops; struct perf_counter *counter; + long err; counter = kzalloc(sizeof(*counter), gfpflags); if (!counter) - return NULL; + return ERR_PTR(-ENOMEM); /* * Single counters are their own group leaders, with an @@ -2505,12 +2506,18 @@ perf_counter_alloc(struct perf_counter_h hw_ops = tp_perf_counter_init(counter); break; } +done: + err = 0; + if (!hw_ops) + err = -EINVAL; + else if (IS_ERR(hw_ops)) + err = PTR_ERR(hw_ops); - if (!hw_ops) { + if (err) { kfree(counter); - return NULL; + return ERR_PTR(err); } -done: + counter->hw_ops = hw_ops; return counter; @@ -2583,10 +2590,10 @@ SYSCALL_DEFINE5(perf_counter_open, goto err_put_context; } - ret = -EINVAL; counter = perf_counter_alloc(&hw_event, cpu, ctx, group_leader, GFP_KERNEL); - if (!counter) + ret = PTR_ERR(counter); + if (IS_ERR(counter)) goto err_put_context; ret = anon_inode_getfd("[perf_counter]", &perf_fops, counter, 0); @@ -2658,8 +2665,8 @@ inherit_counter(struct perf_counter *par child_counter = perf_counter_alloc(&parent_counter->hw_event, parent_counter->cpu, child_ctx, group_leader, GFP_KERNEL); - if (!child_counter) - return NULL; + if (IS_ERR(child_counter)) + return child_counter; /* * Link it up in the child's context: @@ -2710,15 +2717,17 @@ static int inherit_group(struct perf_cou { struct perf_counter *leader; struct perf_counter *sub; + struct perf_counter *child_ctr; leader = inherit_counter(parent_counter, parent, parent_ctx, child, NULL, child_ctx); - if (!leader) - return -ENOMEM; + if (IS_ERR(leader)) + return PTR_ERR(leader); list_for_each_entry(sub, &parent_counter->sibling_list, list_entry) { - if (!inherit_counter(sub, parent, parent_ctx, - child, leader, child_ctx)) - return -ENOMEM; + child_ctr = inherit_counter(sub, parent, parent_ctx, + child, leader, child_ctx); + if (IS_ERR(child_ctr)) + return PTR_ERR(child_ctr); } return 0; } --