The following commit has been merged in the linux branch: commit c0868934e536e0ff508f2d359d006b25abc4970d Author: Robert Richter robert.richter@amd.com Date: Fri Oct 9 03:17:44 2009 +0200

oprofile: warn on freeing event buffer too early

A race shouldn't happen since all workqueues or handlers are canceled or flushed before the event buffer is freed. A warning is triggered now if the buffer is freed too early.

Also, this patch adds some comments about event buffer protection, reworks some code and adds code to clear buffer_pos during alloc and free of the event buffer.

Cc: David Rientjes rientjes@google.com Cc: Stephane Eranian eranian@google.com Signed-off-by: Robert Richter robert.richter@amd.com

diff --git a/drivers/oprofile/event_buffer.c b/drivers/oprofile/event_buffer.c index c38adb3..5df60a6 100644 --- a/drivers/oprofile/event_buffer.c +++ b/drivers/oprofile/event_buffer.c @@ -35,17 +35,22 @@ static size_t buffer_pos; /* atomic_t because wait_event checks it outside of buffer_mutex */ static atomic_t buffer_ready = ATOMIC_INIT(0);

-/* Add an entry to the event buffer. When we - * get near to the end we wake up the process - * sleeping on the read() of the file. +/* + * Add an entry to the event buffer. When we get near to the end we + * wake up the process sleeping on the read() of the file. To protect + * the event_buffer this function may only be called when buffer_mutex + * is set. */ void add_event_entry(unsigned long value) { /* - * catch potential error + * This shouldn't happen since all workqueues or handlers are + * canceled or flushed before the event buffer is freed. */ - if (!event_buffer) + if (!event_buffer) { + WARN_ON_ONCE(1); return; + }

if (buffer_pos == buffer_size) { atomic_inc(&oprofile_stats.event_lost_overflow); @@ -75,7 +80,6 @@ void wake_up_buffer_waiter(void)

int alloc_event_buffer(void) { - int err = -ENOMEM; unsigned long flags;

spin_lock_irqsave(&oprofilefs_lock, flags); @@ -86,13 +90,12 @@ int alloc_event_buffer(void) if (buffer_watershed >= buffer_size) return -EINVAL;

+ buffer_pos = 0; event_buffer = vmalloc(sizeof(unsigned long) * buffer_size); if (!event_buffer) - goto out; + return -ENOMEM;

- err = 0; -out: - return err; + return 0; }

@@ -100,6 +103,7 @@ void free_event_buffer(void) { mutex_lock(&buffer_mutex); vfree(event_buffer); + buffer_pos = 0; event_buffer = NULL; mutex_unlock(&buffer_mutex); } @@ -174,6 +178,7 @@ static ssize_t event_buffer_read(struct file *file, char __user *buf,

mutex_lock(&buffer_mutex);

+ /* May happen if the buffer is freed during pending reads. */ if (!event_buffer) { retval = -EINTR; goto out;