hw_breakpoints: Release the bp slot if arch_validate_hwbkpt_settings() fails.

On a given architecture, when hardware breakpoint registration fails
due to un-supported access type (read/write/execute), we lose the bp
slot since register_perf_hw_breakpoint() does not release the bp slot
on failure.
Hence, any subsequent hardware breakpoint registration starts failing
with 'no space left on device' error.

This patch introduces error handling in register_perf_hw_breakpoint()
function and releases bp slot on error.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: K. Prasad <prasad@linux.vnet.ibm.com>
Cc: Maneesh Soni <maneesh@in.ibm.com>
LKML-Reference: <20100121125516.GA32521@in.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

kernel/hw_breakpoint.c

@@ -296,6 +296,10 @@ int register_perf_hw_breakpoint(struct perf_event *bp)
 	if (!bp->attr.disabled || !bp->overflow_handler)
 		ret = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
 
+	/* if arch_validate_hwbkpt_settings() fails then release bp slot */
+	if (ret)
+		release_bp_slot(bp);
+
 	return ret;
 }