linux-kernel - [PATCH] Revert "random: Mix cputime from each thread that exits to the pool"

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Date:	Mon,  4 Mar 2013 00:03:28 -0800
From:	Russ Dill <russ.dill@...il.com>
To:	stable@...nel.org, linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Nick Kossifidis <mickflemm@...il.com>,
	Theodore Ts'o <tytso@....edu>
Subject: [PATCH] Revert "random: Mix cputime from each thread that exits to the pool"

This reverts commit 6133705494bb02953e1e2cc3018a4373981b3c97.

The above commit introduces a circular locking dependacy. Existing code
takes nonblocking_port.lock and then tasklist_lock. The code in this
commit takes nonblocking_port.lock while talklist_lock is already held
leading to a potential deadlock. For now, simply revert the commit.

Existing lock order:

send_sigio /* takes read lock on tasklist_lock */
kill_fasync_rcu
kill_fasync
account /* takes nonblocking_pool.lock */
extract_entropy
get_random_bytes
create_elf_tables
load_elf_binary
load_elf_library
search_binary_handler

New code:

mix_pool_bytes /* takes nonblocking_pool.lock */
add_device_randomness
posix_cpu_timers_exit
__exit_signal
release_task /* takes write lock on tasklist_lock */
do_exit
__module_put_and_exit
cryptomgr_test

Signed-off-by: Russ Dill <Russ.Dill@...il.com>
---
 kernel/posix-cpu-timers.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 942ca27..1f2ef3d 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -9,7 +9,6 @@
 #include <asm/uaccess.h>
 #include <linux/kernel_stat.h>
 #include <trace/events/timer.h>
-#include <linux/random.h>
 
 /*
  * Called after updating RLIMIT_CPU to run cpu timer and update
@@ -471,8 +470,6 @@ static void cleanup_timers(struct list_head *head,
  */
 void posix_cpu_timers_exit(struct task_struct *tsk)
 {
-	add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
-						sizeof(unsigned long long));
 	cleanup_timers(tsk->cpu_timers,
 		       tsk->utime, tsk->stime, tsk->se.sum_exec_runtime);
 
-- 
1.8.1.2

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