clocksource_lock is used in softirq-context via e.g.
timeofday_periodic_hook() -> get_next_clocksource(), but the lock is not
acquired in a softirq-safe manner - which could lead to deadlocks.
this bug was found via the lock validator i'm working on:
============================
[ BUG: illegal lock usage! ]
----------------------------
illegal {used-in-softirq} -> {enabled-softirqs} usage.
swapper/1 [HC0[0]:SC0[0]:HE1:SE1] takes {clocksource_lock [u:21]}, at:
[<c013f526>] register_clocksource+0x16/0xf0
{used-in-softirq} state was registered at:
[<c013f22d>] get_next_clocksource+0xd/0x40
hardirqs last enabled at: [<c011d31a>] vprintk+0x28a/0x3e0
softirqs last enabled at: [<c0122999>] irq_exit+0x39/0x50
other info that might help in debugging this:
------------------------------
| showing all locks held by: | (swapper/1 [c30d7790, 125]): <none>
------------------------------
[<c010432d>] show_trace+0xd/0x10
[<c0104347>] dump_stack+0x17/0x20
[<c01379b2>] print_usage_bug+0x1e2/0x200
[<c013817d>] mark_lock+0x28d/0x2a0
[<c0138835>] debug_lock_chain+0x6a5/0x10d0
[<c013929d>] debug_lock_chain_spin+0x3d/0x60
[<c026570d>] _raw_spin_lock+0x2d/0x90
[<c04d88d8>] _spin_lock+0x8/0x10
[<c013f526>] register_clocksource+0x16/0xf0
[<c0681137>] init_pit_clocksource+0x57/0x90
[<c01003fa>] init+0xfa/0x3e0
[<c0100ef5>] kernel_thread_helper+0x5/0x10
the fix is to lock clocksource_lock in a softirq-safe way.
(with this patch applied, the timeofday code validates fine.)
Signed-off-by: Ingo Molnar <[email protected]>
----
kernel/time/clocksource.c | 31 +++++++++++++++++--------------
1 files changed, 17 insertions(+), 14 deletions(-)
Index: linux/kernel/time/clocksource.c
===================================================================
--- linux.orig/kernel/time/clocksource.c
+++ linux/kernel/time/clocksource.c
@@ -48,6 +48,9 @@ extern struct clocksource clocksource_ji
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *next_clocksource;
static LIST_HEAD(clocksource_list);
+/*
+ * May be used in softirq context too:
+ */
static DEFINE_SPINLOCK(clocksource_lock);
static char override_name[32];
@@ -70,12 +73,12 @@ late_initcall(clocksource_done_booting);
*/
struct clocksource *get_next_clocksource(void)
{
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
if (next_clocksource && finished_booting) {
curr_clocksource = next_clocksource;
next_clocksource = NULL;
}
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
return curr_clocksource;
}
@@ -141,7 +144,7 @@ static int is_registered_source(struct c
*/
void register_clocksource(struct clocksource *c)
{
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
/* check if clocksource is already registered */
if (is_registered_source(c)) {
@@ -152,7 +155,7 @@ void register_clocksource(struct clockso
/* select next clocksource */
next_clocksource = select_clocksource();
}
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
}
EXPORT_SYMBOL(register_clocksource);
@@ -166,9 +169,9 @@ EXPORT_SYMBOL(register_clocksource);
*/
void reselect_clocksource(void)
{
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
next_clocksource = select_clocksource();
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
}
/**
@@ -183,9 +186,9 @@ sysfs_show_current_clocksources(struct s
{
char *curr = buf;
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
curr += sprintf(curr, "%s ", curr_clocksource->name);
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
curr += sprintf(curr, "\n");
@@ -214,7 +217,7 @@ static ssize_t sysfs_override_clocksourc
if (count < 1)
return -EINVAL;
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
/* copy the name given: */
memcpy(override_name, buf, count);
@@ -223,7 +226,7 @@ static ssize_t sysfs_override_clocksourc
/* try to select it: */
next_clocksource = select_clocksource();
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
return count;
}
@@ -241,14 +244,14 @@ sysfs_show_available_clocksources(struct
struct list_head *tmp;
char *curr = buf;
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
list_for_each(tmp, &clocksource_list) {
struct clocksource *src;
src = list_entry(tmp, struct clocksource, list);
curr += sprintf(curr, "%s ", src->name);
}
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
curr += sprintf(curr, "\n");
@@ -301,10 +304,10 @@ device_initcall(init_clocksource_sysfs);
*/
static int __init boot_override_clocksource(char* str)
{
- spin_lock(&clocksource_lock);
+ spin_lock_bh(&clocksource_lock);
if (str)
strlcpy(override_name, str, sizeof(override_name));
- spin_unlock(&clocksource_lock);
+ spin_unlock_bh(&clocksource_lock);
return 1;
}
On Wed, 2006-01-25 at 19:00 +0100, Ingo Molnar wrote:
> clocksource_lock is used in softirq-context via e.g.
> timeofday_periodic_hook() -> get_next_clocksource(), but the lock is not
> acquired in a softirq-safe manner - which could lead to deadlocks.
Nice catch. Andrew also noticed this issue just a few hours before you
sent this. Great minds...
> this bug was found via the lock validator i'm working on:
>
> ============================
> [ BUG: illegal lock usage! ]
> ----------------------------
> illegal {used-in-softirq} -> {enabled-softirqs} usage.
> swapper/1 [HC0[0]:SC0[0]:HE1:SE1] takes {clocksource_lock [u:21]}, at:
> [<c013f526>] register_clocksource+0x16/0xf0
> {used-in-softirq} state was registered at:
> [<c013f22d>] get_next_clocksource+0xd/0x40
> hardirqs last enabled at: [<c011d31a>] vprintk+0x28a/0x3e0
> softirqs last enabled at: [<c0122999>] irq_exit+0x39/0x50
>
> other info that might help in debugging this:
> ------------------------------
> | showing all locks held by: | (swapper/1 [c30d7790, 125]): <none>
> ------------------------------
>
> [<c010432d>] show_trace+0xd/0x10
> [<c0104347>] dump_stack+0x17/0x20
> [<c01379b2>] print_usage_bug+0x1e2/0x200
> [<c013817d>] mark_lock+0x28d/0x2a0
> [<c0138835>] debug_lock_chain+0x6a5/0x10d0
> [<c013929d>] debug_lock_chain_spin+0x3d/0x60
> [<c026570d>] _raw_spin_lock+0x2d/0x90
> [<c04d88d8>] _spin_lock+0x8/0x10
> [<c013f526>] register_clocksource+0x16/0xf0
> [<c0681137>] init_pit_clocksource+0x57/0x90
> [<c01003fa>] init+0xfa/0x3e0
> [<c0100ef5>] kernel_thread_helper+0x5/0x10
>
> the fix is to lock clocksource_lock in a softirq-safe way.
>
> (with this patch applied, the timeofday code validates fine.)
I'm getting lots of local_bh_disable warnings with this patch on my
timeofday tree (interrupts are disabled in timefoday_periodic_hook which
calls get_next_clocksource). Wouldn't using spin_lock_irqsave/restore be
better here (seems to work for me)?
thanks
-john