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author | Greg Thelen <gthelen@google.com> | 2010-11-15 10:20:52 +0100 |
---|---|---|
committer | Jens Axboe <jaxboe@fusionio.com> | 2010-11-15 10:23:31 +0100 |
commit | d69b78ba1deaaa95ffa8dac5a9ca819ce454d52e (patch) | |
tree | 75b6df8731e08a102d54163b196835e189978fc1 /fs | |
parent | 1ff5125fb85a46279421350eeaf812f728784d35 (diff) | |
download | kernel_samsung_smdk4412-d69b78ba1deaaa95ffa8dac5a9ca819ce454d52e.zip kernel_samsung_smdk4412-d69b78ba1deaaa95ffa8dac5a9ca819ce454d52e.tar.gz kernel_samsung_smdk4412-d69b78ba1deaaa95ffa8dac5a9ca819ce454d52e.tar.bz2 |
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')
-rw-r--r-- | fs/ioprio.c | 31 |
1 files changed, 6 insertions, 25 deletions
diff --git a/fs/ioprio.c b/fs/ioprio.c index 2f7d05c..7da2a06 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; } |