lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 11 Dec 2015 16:16:37 -0800 (PST) From: Ani Sinha <ani@...sta.com> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> cc: Rik van Riel <riel@...hat.com>, Ani Sinha <ani@...sta.com>, Randy Dunlap <rdunlap@...radead.org>, Richard Weinberger <richard@....at>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Ivan Delalande <colona@...sta.com>, fruggeri <fruggeri@...sta.com> Subject: Re: new warning on sysrq kernel crash trigger On Fri, 11 Dec 2015, Paul E. McKenney wrote: > On Fri, Dec 11, 2015 at 05:10:43PM -0500, Rik van Riel wrote: > > On 12/11/2015 03:44 PM, Ani Sinha wrote: > > > > > > > > > On Thu, 10 Dec 2015, Paul E. McKenney wrote: > > > > > >> On Thu, Dec 10, 2015 at 03:57:09PM -0800, Ani Sinha wrote: > > >>> Hi guys > > >>> > > >>> I am noticing a new warning in linux 3.18 which we did not see before > > >>> in linux 3.4 : > > >>> > > >>> bash-4.1# echo c > /proc/sysrq-trigger > > >>> [ 978.807185] BUG: sleeping function called from invalid context at > > >>> ../arch/x86/mm/fault.c:1187 > > >>> [ 978.909816] in_atomic(): 0, irqs_disabled(): 0, pid: 4706, name: bash > > >>> [ 978.987358] Preemption disabled at:[<ffffffff81484339>] printk+0x48/0x4a > > >>> > > >>> > > >>> I have bisected this to the following change : > > >>> > > >>> commit 984d74a72076a12b400339973e8c98fd2fcd90e5 > > >>> Author: Rik van Riel <riel@...hat.com> > > >>> Date: Fri Jun 6 14:38:13 2014 -0700 > > >>> > > >>> sysrq: rcu-ify __handle_sysrq > > >>> > > >>> > > >>> the rcu_read_lock() in handle_sysrq() bumps up > > >>> current->rcu_read_lock_nesting. Hence, in __do_page_fault() when it > > >>> calls might_sleep() in x86/mm/fault.c line 1191, > > >>> preempt_count_equals(0) returns false and hence the warning is > > >>> printed. > > >>> > > >>> One way to handle this would be to do something like this: > > >>> > > >>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > > >>> index eef44d9..d4dbe22 100644 > > >>> --- a/arch/x86/mm/fault.c > > >>> +++ b/arch/x86/mm/fault.c > > >>> @@ -1132,7 +1132,7 @@ __do_page_fault(struct pt_regs *regs, unsigned > > >>> long error_code, > > >>> * If we're in an interrupt, have no user context or are running > > >>> * in a region with pagefaults disabled then we must not take the fault > > >>> */ > > >>> - if (unlikely(faulthandler_disabled() || !mm)) { > > >>> + if (unlikely(faulthandler_disabled() || rcu_preempt_depth() || !mm)) { > > >> > > >> This works if CONFIG_PREEMPT=y, but if CONFIG_PREEMPT=n, then > > >> rcu_preempt_depth() unconditionally returns zero. And if > > >> CONFIG_PREEMPT_COUNT=y && CONFIG_PREEMPT=n, you would still see > > >> the might_sleep() splat. > > >> > > >> Maybe use SRCU instead of RCU for this purpose? > > >> > > > > > > From ae232ce3fb167b2ad363bfac7aab69001bc55a50 Mon Sep 17 00:00:00 2001 > > > From: Ani Sinha <ani@...sta.com> > > > Date: Fri, 11 Dec 2015 12:07:42 -0800 > > > Subject: [PATCH 1/1] Fix 'sleeping function called from invalid context' > > > warning in sysrq generated crash. > > > > > > Commit 984d74a72076a1 ("sysrq: rcu-ify __handle_sysrq") > > > replaced spin_lock_irqsave() calls with > > > rcu_read_lock() calls in sysrq. Since rcu_read_lock() does not > > > disable preemption, faulthandler_disabled() in > > > __do_page_fault() in x86/fault.c returns false. When the code > > > later calls might_sleep() in the pagefault handler, we get the > > > following warning: > > > > > > BUG: sleeping function called from invalid context at ../arch/x86/mm/fault.c:1187 > > > in_atomic(): 0, irqs_disabled(): 0, pid: 4706, name: bash > > > Preemption disabled at:[<ffffffff81484339>] printk+0x48/0x4a > > > > > > To fix this, replace RCU call in handle_sysrq() to use SRCU. > > > > The sysrq code can be called from irq context. > > > > Trying to use SRCU from an irq context sounds like it could > > be a bad idea, though admittedly I do not know enough about > > SRCU to know for sure :) > > Indeed, not the best idea! ;-) > > I could imagine something like this: > > if (in_irq()) > rcu_read_lock(); > else > idx = srcu_read_lock(&sysrq_rcu); > > And ditto for unlock. Then, for the update: > > synchronize_rcu_mult(call_rcu, call_sysrq_srcu); > > Where: > > static void call_sysrq_srcu(struct rcu_head *head, rcu_callback_t func) > { > call_srcu(&sysrq_rcu, head, func); > } > >From ae232ce3fb167b2ad363bfac7aab69001bc55a50 Mon Sep 17 00:00:00 2001 From: Ani Sinha <ani@...sta.com> Date: Fri, 11 Dec 2015 12:07:42 -0800 Subject: [PATCH 1/1] Fix 'sleeping function called from invalid context' warning in sysrq generated crash. Commit 984d74a72076a1 ("sysrq: rcu-ify __handle_sysrq") replaced spin_lock_irqsave() calls with rcu_read_lock() calls in sysrq. Since rcu_read_lock() does not disable preemption, faulthandler_disabled() in __do_page_fault() in x86/fault.c returns false. When the code later calls might_sleep() in the pagefault handler, we get the following warning: BUG: sleeping function called from invalid context at ../arch/x86/mm/fault.c:1187 in_atomic(): 0, irqs_disabled(): 0, pid: 4706, name: bash Preemption disabled at:[<ffffffff81484339>] printk+0x48/0x4a To fix this, replace RCU call in handle_sysrq() to use SRCU in non-irq context. Tested this patch on linux 3.18 by booting off one of our boards. Fixes: 984d74a72076a1 ("sysrq: rcu-ify __handle_sysrq") Signed-off-by: Ani Sinha <ani@...sta.com> --- diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 5381a72..df7d747 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -54,6 +54,7 @@ /* Whether we react on sysrq keys or just ignore them */ static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE; static bool __read_mostly sysrq_always_enabled; +DEFINE_STATIC_SRCU(sysrq_rcu); static bool sysrq_on(void) { @@ -519,10 +520,13 @@ void __handle_sysrq(int key, bool check_mask) { struct sysrq_key_op *op_p; int orig_log_level; - int i; + int i, idx; rcu_sysrq_start(); - rcu_read_lock(); + if (in_irq()) + rcu_read_lock(); + else + idx = srcu_read_lock(&sysrq_rcu); /* * Raise the apparent loglevel to maximum so that the sysrq header * is shown to provide the user with positive feedback. We do not @@ -564,7 +568,10 @@ void __handle_sysrq(int key, bool check_mask) pr_cont("\n"); console_loglevel = orig_log_level; } - rcu_read_unlock(); + if (in_irq()) + rcu_read_unlock(); + else + srcu_read_unlock(&sysrq_rcu, idx); rcu_sysrq_end(); } @@ -1040,6 +1047,11 @@ int sysrq_toggle_support(int enable_mask) return 0; } +static void call_sysrq_srcu(struct rcu_head *head, rcu_callback_t func) +{ + call_srcu(&sysrq_rcu, head, func); +} + static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p, struct sysrq_key_op *remove_op_p) { @@ -1059,7 +1071,7 @@ static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p, * Wait for it to go away before returning, so the code for an old * op is not freed (eg. on module unload) while it is in use. */ - synchronize_rcu(); + synchronize_rcu_mult(call_rcu, call_sysrq_srcu); return retval; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists