Messages in this thread Patch in this message | | | Date | Tue, 2 Nov 2010 12:15:30 +0000 | Subject | [2.6.37-rc1] sys_ioprio_set and RCU locking... | From | Daniel J Blueman <> |
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With 2.6.37-rc1, I observe sys_ioprio_set not taking the RCU lock [1] across access to the task credentials.
Inspecting the code in fs/ioprio.c, the tasklist_lock is held for read across the __task_cred call, which is presumably sufficient to prevent the task credentials becoming stale.
Thus, is there preference to take the RCU lock for read across the credential access eg at [2], or annotate the call?
Thanks, Daniel
--- [1]
===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
kernel/pid.c:419 invoked rcu_dereference_check() without protection!
other info that might help us debug this:
rcu_scheduler_active = 1, debug_locks = 1
1 lock held by start-stop-daem/2246:
#0: (tasklist_lock){.?.?..}, at: [<ffffffff811a2dfa>] sys_ioprio_set+0x8a/0x400
stack backtrace:
Pid: 2246, comm: start-stop-daem Not tainted 2.6.37-rc1-330cd+ #2
Call Trace:
[<ffffffff8109f5f4>] lockdep_rcu_dereference+0xa4/0xc0
[<ffffffff81085651>] find_task_by_pid_ns+0x81/0x90
[<ffffffff8108567d>] find_task_by_vpid+0x1d/0x20
[<ffffffff811a3160>] sys_ioprio_set+0x3f0/0x400
[<ffffffff816efa79>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff81003482>] system_call_fastpath+0x16/0x1b
--- [2]
Take the RCU lock for read across acquiring the pointer to the task credentials and dereferencing it.
Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>
diff --git a/fs/ioprio.c b/fs/ioprio.c index 748cfb9..00cc0e5 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -139,8 +139,10 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) break;
do_each_thread(g, p) { + rcu_read_lock(); if (__task_cred(p)->uid != who) continue; + rcu_read_unlock(); ret = set_task_ioprio(p, ioprio); if (ret) goto free_uid; @@ -232,8 +234,10 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) break;
do_each_thread(g, p) { + rcu_read_lock(); if (__task_cred(p)->uid != user->uid) continue; + rcu_read_unlock(); tmpio = get_task_ioprio(p); if (tmpio < 0) continue; -- Daniel J Blueman
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