Commit d69b78ba1deaaa95ffa8dac5a9ca819ce454d52e
Committed by
Jens Axboe
Jens Axboe
1 parent
1ff5125fb8
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>
Showing 1 changed file with 6 additions and 25 deletions Side-by-side Diff
fs/ioprio.c
| ... | ... | @@ -103,22 +103,15 @@ |
| 103 | 103 | } |
| 104 | 104 | |
| 105 | 105 | ret = -ESRCH; |
| 106 | - /* | |
| 107 | - * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic", | |
| 108 | - * so we can't use rcu_read_lock(). See re-copy of ->ioprio | |
| 109 | - * in copy_process(). | |
| 110 | - */ | |
| 111 | - read_lock(&tasklist_lock); | |
| 106 | + rcu_read_lock(); | |
| 112 | 107 | switch (which) { |
| 113 | 108 | case IOPRIO_WHO_PROCESS: |
| 114 | - rcu_read_lock(); | |
| 115 | 109 | if (!who) |
| 116 | 110 | p = current; |
| 117 | 111 | else |
| 118 | 112 | p = find_task_by_vpid(who); |
| 119 | 113 | if (p) |
| 120 | 114 | ret = set_task_ioprio(p, ioprio); |
| 121 | - rcu_read_unlock(); | |
| 122 | 115 | break; |
| 123 | 116 | case IOPRIO_WHO_PGRP: |
| 124 | 117 | if (!who) |
| ... | ... | @@ -141,12 +134,7 @@ |
| 141 | 134 | break; |
| 142 | 135 | |
| 143 | 136 | do_each_thread(g, p) { |
| 144 | - int match; | |
| 145 | - | |
| 146 | - rcu_read_lock(); | |
| 147 | - match = __task_cred(p)->uid == who; | |
| 148 | - rcu_read_unlock(); | |
| 149 | - if (!match) | |
| 137 | + if (__task_cred(p)->uid != who) | |
| 150 | 138 | continue; |
| 151 | 139 | ret = set_task_ioprio(p, ioprio); |
| 152 | 140 | if (ret) |
| ... | ... | @@ -160,7 +148,7 @@ |
| 160 | 148 | ret = -EINVAL; |
| 161 | 149 | } |
| 162 | 150 | |
| 163 | - read_unlock(&tasklist_lock); | |
| 151 | + rcu_read_unlock(); | |
| 164 | 152 | return ret; |
| 165 | 153 | } |
| 166 | 154 | |
| 167 | 155 | |
| 168 | 156 | |
| ... | ... | @@ -204,17 +192,15 @@ |
| 204 | 192 | int ret = -ESRCH; |
| 205 | 193 | int tmpio; |
| 206 | 194 | |
| 207 | - read_lock(&tasklist_lock); | |
| 195 | + rcu_read_lock(); | |
| 208 | 196 | switch (which) { |
| 209 | 197 | case IOPRIO_WHO_PROCESS: |
| 210 | - rcu_read_lock(); | |
| 211 | 198 | if (!who) |
| 212 | 199 | p = current; |
| 213 | 200 | else |
| 214 | 201 | p = find_task_by_vpid(who); |
| 215 | 202 | if (p) |
| 216 | 203 | ret = get_task_ioprio(p); |
| 217 | - rcu_read_unlock(); | |
| 218 | 204 | break; |
| 219 | 205 | case IOPRIO_WHO_PGRP: |
| 220 | 206 | if (!who) |
| ... | ... | @@ -241,12 +227,7 @@ |
| 241 | 227 | break; |
| 242 | 228 | |
| 243 | 229 | do_each_thread(g, p) { |
| 244 | - int match; | |
| 245 | - | |
| 246 | - rcu_read_lock(); | |
| 247 | - match = __task_cred(p)->uid == user->uid; | |
| 248 | - rcu_read_unlock(); | |
| 249 | - if (!match) | |
| 230 | + if (__task_cred(p)->uid != user->uid) | |
| 250 | 231 | continue; |
| 251 | 232 | tmpio = get_task_ioprio(p); |
| 252 | 233 | if (tmpio < 0) |
| ... | ... | @@ -264,7 +245,7 @@ |
| 264 | 245 | ret = -EINVAL; |
| 265 | 246 | } |
| 266 | 247 | |
| 267 | - read_unlock(&tasklist_lock); | |
| 248 | + rcu_read_unlock(); | |
| 268 | 249 | return ret; |
| 269 | 250 | } |