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authorGreg Thelen <gthelen@google.com>2010-11-15 10:20:52 +0100
committerJens Axboe <jaxboe@fusionio.com>2010-11-15 10:23:31 +0100
commitd69b78ba1deaaa95ffa8dac5a9ca819ce454d52e (patch)
tree75b6df8731e08a102d54163b196835e189978fc1 /fs/ioprio.c
parent1ff5125fb85a46279421350eeaf812f728784d35 (diff)
downloadlinux-d69b78ba1deaaa95ffa8dac5a9ca819ce454d52e.tar.gz
ioprio: grab rcu_read_lock in sys_ioprio_{set,get}()
Using: - CONFIG_LOCKUP_DETECTOR=y - CONFIG_PREEMPT=y - CONFIG_LOCKDEP=y - CONFIG_PROVE_LOCKING=y - CONFIG_PROVE_RCU=y found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm: =================================================== [ 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 = 0 1 lock held by ureadahead/1355: #0: (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e stack backtrace: Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1 Call Trace: [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3 [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24 [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f The fix is to: a) grab rcu lock in sys_ioprio_{set,get}() and b) avoid grabbing tasklist_lock. Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889 Signed-off-by: Greg Thelen <gthelen@google.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Modified by Jens to remove the now redundant inner rcu lock and unlock since they are now protected by the outer lock. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'fs/ioprio.c')
-rw-r--r--fs/ioprio.c31
1 files changed, 6 insertions, 25 deletions
diff --git a/fs/ioprio.c b/fs/ioprio.c
index 2f7d05c8992..7da2a06508e 100644
--- a/fs/ioprio.c
+++ b/fs/ioprio.c
@@ -103,22 +103,15 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
}
ret = -ESRCH;
- /*
- * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
- * so we can't use rcu_read_lock(). See re-copy of ->ioprio
- * in copy_process().
- */
- read_lock(&tasklist_lock);
+ rcu_read_lock();
switch (which) {
case IOPRIO_WHO_PROCESS:
- rcu_read_lock();
if (!who)
p = current;
else
p = find_task_by_vpid(who);
if (p)
ret = set_task_ioprio(p, ioprio);
- rcu_read_unlock();
break;
case IOPRIO_WHO_PGRP:
if (!who)
@@ -141,12 +134,7 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
break;
do_each_thread(g, p) {
- int match;
-
- rcu_read_lock();
- match = __task_cred(p)->uid == who;
- rcu_read_unlock();
- if (!match)
+ if (__task_cred(p)->uid != who)
continue;
ret = set_task_ioprio(p, ioprio);
if (ret)
@@ -160,7 +148,7 @@ free_uid:
ret = -EINVAL;
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return ret;
}
@@ -204,17 +192,15 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
int ret = -ESRCH;
int tmpio;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
switch (which) {
case IOPRIO_WHO_PROCESS:
- rcu_read_lock();
if (!who)
p = current;
else
p = find_task_by_vpid(who);
if (p)
ret = get_task_ioprio(p);
- rcu_read_unlock();
break;
case IOPRIO_WHO_PGRP:
if (!who)
@@ -241,12 +227,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
break;
do_each_thread(g, p) {
- int match;
-
- rcu_read_lock();
- match = __task_cred(p)->uid == user->uid;
- rcu_read_unlock();
- if (!match)
+ if (__task_cred(p)->uid != user->uid)
continue;
tmpio = get_task_ioprio(p);
if (tmpio < 0)
@@ -264,6 +245,6 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
ret = -EINVAL;
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return ret;
}