diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-06-21 23:56:16 +0530 |
|---|---|---|
| committer | Mister Oyster <oysterized@gmail.com> | 2017-04-11 10:59:13 +0200 |
| commit | c873d392b1c911e75aada1586d073d05cbbc6ed8 (patch) | |
| tree | 81c186046eaac96aee224f10b54672cd9e9ea2ec /kernel/rcutree.c | |
| parent | 41e1172898c515ada8580bbaec7713253cfaa241 (diff) | |
rcu: Prevent spurious-wakeup DoS attack on rcu_gp_kthread()
Spurious wakeups in the force-quiescent-state loop in rcu_gp_kthread()
cause the timeout to be recalculated, which would prevent rcu_gp_fqs()
from ever being called. This would in turn would prevent the grace period
from ever ending for as long as there was at least one CPU in an extended
quiescent state that had not yet passed through a quiescent state.
This commit therefore avoids recalculating the timeout unless the
previous pass's call to wait_event_interruptible_timeout() actually
did time out, thus preventing the above scenario.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Git-commit: 88d6df612cc3c99f56cc18461fcc531c3a145544
[kishank@codeaurora.org resolve trivial conflicts]
Signed-off-by: Kishan Kumar <kishank@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Change-Id: I43f22a80d4334ea5a7105a6da6f929239df76a11
Diffstat (limited to 'kernel/rcutree.c')
| -rw-r--r-- | kernel/rcutree.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6c0c5ede0..847b69efe 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1495,6 +1495,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) static int __noreturn rcu_gp_kthread(void *arg) { int fqs_state; + int gf; unsigned long j; int ret; struct rcu_state *rsp = arg; @@ -1521,10 +1522,13 @@ static int __noreturn rcu_gp_kthread(void *arg) j = HZ; jiffies_till_first_fqs = HZ; } + ret = 0; for (;;) { - rsp->jiffies_force_qs = jiffies + j; + if (!ret) + rsp->jiffies_force_qs = jiffies + j; ret = wait_event_interruptible_timeout(rsp->gp_wq, - (rsp->gp_flags & RCU_GP_FLAG_FQS) || + ((gf = ACCESS_ONCE(rsp->gp_flags)) & + RCU_GP_FLAG_FQS) || (!ACCESS_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)), j); @@ -1533,7 +1537,8 @@ static int __noreturn rcu_gp_kthread(void *arg) !rcu_preempt_blocked_readers_cgp(rnp)) break; /* If time for quiescent-state forcing, do it. */ - if (ret == 0 || (rsp->gp_flags & RCU_GP_FLAG_FQS)) { + if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) || + (gf & RCU_GP_FLAG_FQS)) { fqs_state = rcu_gp_fqs(rsp, fqs_state); cond_resched(); } else { |