Messages in this thread Patch in this message | | | Subject | Re: [PATCH] printk: fix recursion of logbuf_lock spinlock | From | Peter Zijlstra <> | Date | Fri, 25 Nov 2011 12:49:06 +0100 |
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On Thu, 2011-11-24 at 20:04 +0100, Andrea Arcangeli wrote: > kernel/printk.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/printk.c b/kernel/printk.c > index 1455a0d..fc3c831 100644 > --- a/kernel/printk.c > +++ b/kernel/printk.c > @@ -1259,9 +1259,9 @@ void console_unlock(void) > > console_may_schedule = 0; > > -again: > for ( ; ; ) { > raw_spin_lock_irqsave(&logbuf_lock, flags); > +again: > wake_klogd |= log_start - log_end; > if (con_start == log_end) > break; /* Nothing to print */
The better change would be the below one, since that avoid doing console_trylock() while holding logbuf_lock. The problem is that console_trylock() can do up() and thus result in a wakeup while holding logbuf_lock and we're trying to get rid of locks nested under logbug_lock.
--- Subject: printk: Avoid double lock acquire
Commit 4f2a8d3cf5e ("printk: Fix console_sem vs logbuf_lock unlock race") introduced another silly bug where we would want to acquire an already held lock. Avoid this.
Reported-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- kernel/printk.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/kernel/printk.c b/kernel/printk.c index dfd8f73..187662f 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1292,10 +1292,11 @@ void console_unlock(void) raw_spin_lock(&logbuf_lock); if (con_start != log_end) retry = 1; + raw_spin_unlock_irqrestore(&logbuf_lock, flags); + if (retry && console_trylock()) goto again; - raw_spin_unlock_irqrestore(&logbuf_lock, flags); if (wake_klogd) wake_up_klogd(); }
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