Attachment 296255 Details for Bug 432979 – fix to rt_mutex code for printk in atomic (don't really take locks if in printk)

fix to rt_mutex code for printk in atomic (don't really take locks if in printk)

printk-in-atomic-hack-fix.patch (text/x-patch), 1.80 KB, created by Jon Masters on 2008-02-28 20:33:54 UTC

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Creator: Jon Masters

Created: 2008-02-28 20:33:54 UTC

Size: 1.80 KB

patch

obsolete

>From: Steven Rostedt <srostedt@redhat.com>
>Subject: fix printk in atomic hack
>
>The printk in atomic hack had a slight bug. This but was triggered
>by debug locking options. The hack prevents grabbing sleeping spin
>locks in printk console drivers if we are in atomic (can't sleep).
>But the unlock had a bug where it incorrectely assumed that if
>we are in printk and atomic, that we didn't grab the lock. The debug
>locking can encapsulate these options and cause unlocks to be in atomic
>when the lock was not. This means we would not release the lock after
>it was taken.
>
>The patch only skips releasing the lock if in printk - atomic *and*
>not the lock owner.
>
>Special thanks goes to Jon Masters for digging his head deep into
>this crap and narrowing it down to a problem with printks and locks.
>
>Signed-off-by: Steven Rostedt <srostedt@redhat.com>
>---
> kernel/rtmutex.c |    4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>Index: linux-2.6.24.3-rt3/kernel/rtmutex.c
>===================================================================
>--- linux-2.6.24.3-rt3.orig/kernel/rtmutex.c	2008-02-27 13:42:10.000000000 -0500
>+++ linux-2.6.24.3-rt3/kernel/rtmutex.c	2008-02-27 14:11:06.000000000 -0500
>@@ -634,7 +634,7 @@ rt_spin_lock_fastlock(struct rt_mutex *l
> 		void fastcall (*slowfn)(struct rt_mutex *lock))
> {
> 	/* Temporary HACK! */
>-	if (!current->in_printk)
>+	if (likely(!current->in_printk))
> 		might_sleep();
> 	else if (in_atomic() || irqs_disabled())
> 		/* don't grab locks for printk in atomic */
>@@ -651,7 +651,7 @@ rt_spin_lock_fastunlock(struct rt_mutex 
> 			void fastcall (*slowfn)(struct rt_mutex *lock))
> {
> 	/* Temporary HACK! */
>-	if (current->in_printk && (in_atomic() || irqs_disabled()))
>+	if (unlikely(rt_mutex_owner(lock) != current) && current->in_printk)
> 		/* don't grab locks for printk in atomic */
> 		return;
>

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Attachments on bug 432979: 296255 | 304428