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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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2015-09-09 19:06:33 +02:00 committed by Ingo Molnar
parent dfe1f3cb31
commit f55fc2a57c
1 changed files with 32 additions and 17 deletions
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49
kernel/events/core.c
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@ -8297,13 +8297,30 @@ SYSCALL_DEFINE5(perf_event_open,
if (move_group) {
gctx = group_leader->ctx;
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,
@ -8311,13 +8328,7 @@ 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.
@ -8349,22 +8360,20 @@ 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();
@ -8391,6 +8400,12 @@ 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);