Re: [PATCH v2] mm: fix unexpected changes to {failslab|fail_page_alloc}.attr

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

On 2022/11/8 16:44, Wei Yongjun wrote:
> Hi Zheng Qi,
>
> On 2022/11/8 11:52, Qi Zheng wrote:
> > When we specify __GFP_NOWARN, we only expect that no warnings
> > will be issued for current caller. But in the __should_failslab()
> > and __should_fail_alloc_page(), the local GFP flags alter the
> > global {failslab|fail_page_alloc}.attr, which is persistent and
> > shared by all tasks. This is not what we expected, let's fix it.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: 3f913fc5f974 ("mm: fix missing handler for __GFP_NOWARN")
> > Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > ---
> >   v1: https://lore.kernel.org/lkml/20221107033109.59709-1-zhengqi.arch@xxxxxxxxxxxxx/
> >
> >   Changelog in v1 -> v2:
> >    - add comment for __should_failslab() and __should_fail_alloc_page()
> >      (suggested by Jason)
> >
> >   include/linux/fault-inject.h |  7 +++++--
> >   lib/fault-inject.c           | 14 +++++++++-----
> >   mm/failslab.c                | 12 ++++++++++--
> >   mm/page_alloc.c              |  7 +++++--
> >   4 files changed, 29 insertions(+), 11 deletions(-)
> >
> > diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
> > index 9f6e25467844..444236dadcf0 100644
> > --- a/include/linux/fault-inject.h
> > +++ b/include/linux/fault-inject.h
> > @@ -20,7 +20,6 @@ struct fault_attr {
> >   	atomic_t space;
> >   	unsigned long verbose;
> >   	bool task_filter;
> > -	bool no_warn;
> >   	unsigned long stacktrace_depth;
> >   	unsigned long require_start;
> >   	unsigned long require_end;
> > @@ -32,6 +31,10 @@ struct fault_attr {
> >   	struct dentry *dname;
> >   };
> >   
> > +enum fault_flags {
> > +	FAULT_NOWARN =	1 << 0,
> > +};
> > +
> >   #define FAULT_ATTR_INITIALIZER {					\
> >   		.interval = 1,						\
> >   		.times = ATOMIC_INIT(1),				\
> > @@ -40,11 +43,11 @@ struct fault_attr {
> >   		.ratelimit_state = RATELIMIT_STATE_INIT_DISABLED,	\
> >   		.verbose = 2,						\
> >   		.dname = NULL,						\
> > -		.no_warn = false,					\
>
> How about keep no_warn attr as it be, and export it to user?
>
> When testing with fault injection, and each fault will print an backtrace.
> but not all of the testsuit can tell us which one is fault injection
> message or other is a real warning/crash like syzkaller do.
>
> In my case, to make things simple, we usually used a regex to detect whether
> wanring/error happend. So we disabled the slab/page fault warning message by
> default, and only enable it when debug real issue.

So you want to set/clear this no_warn attr through the procfs or sysfs
interface, so that you can easily disable/enable the slab/page fault
warning message from the user mode. Right?

Seems reasonable to me. Anyone else has an opinion on this? If it is
really needed, I can do it later.

Thanks,
Qi

> Regards,
>
>
> >   	}
> >   
> >   #define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
> >   int setup_fault_attr(struct fault_attr *attr, char *str);
> > +bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags);
> >   bool should_fail(struct fault_attr *attr, ssize_t size);
> >   
> >   #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> > diff --git a/lib/fault-inject.c b/lib/fault-inject.c
> > index 4b8fafce415c..5971f7c3e49e 100644
> > --- a/lib/fault-inject.c
> > +++ b/lib/fault-inject.c
> > @@ -41,9 +41,6 @@ EXPORT_SYMBOL_GPL(setup_fault_attr);
> >   
> >   static void fail_dump(struct fault_attr *attr)
> >   {
> > -	if (attr->no_warn)
> > -		return;
> > -
> >   	if (attr->verbose > 0 && __ratelimit(&attr->ratelimit_state)) {
> >   		printk(KERN_NOTICE "FAULT_INJECTION: forcing a failure.\n"
> >   		       "name %pd, interval %lu, probability %lu, "
> > @@ -103,7 +100,7 @@ static inline bool fail_stacktrace(struct fault_attr *attr)
> >    * http://www.nongnu.org/failmalloc/
> >    */
> >   
> > -bool should_fail(struct fault_attr *attr, ssize_t size)
> > +bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags)
> >   {
> >   	bool stack_checked = false;
> >   
> > @@ -152,13 +149,20 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
> >   		return false;
> >   
> >   fail:
> > -	fail_dump(attr);
> > +	if (!(flags & FAULT_NOWARN))
> > +		fail_dump(attr);
> >   
> >   	if (atomic_read(&attr->times) != -1)
> >   		atomic_dec_not_zero(&attr->times);
> >   
> >   	return true;
> >   }
> > +EXPORT_SYMBOL_GPL(should_fail_ex);
> > +
> > +bool should_fail(struct fault_attr *attr, ssize_t size)
> > +{
> > +	return should_fail_ex(attr, size, 0);
> > +}
> >   EXPORT_SYMBOL_GPL(should_fail);
> >   
> >   #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> > diff --git a/mm/failslab.c b/mm/failslab.c
> > index 58df9789f1d2..ffc420c0e767 100644
> > --- a/mm/failslab.c
> > +++ b/mm/failslab.c
> > @@ -16,6 +16,8 @@ static struct {
> >   
> >   bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> >   {
> > +	int flags = 0;
> > +
> >   	/* No fault-injection for bootstrap cache */
> >   	if (unlikely(s == kmem_cache))
> >   		return false;
> > @@ -30,10 +32,16 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> >   	if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
> >   		return false;
> >   
> > +	/*
> > +	 * In some cases, it expects to specify __GFP_NOWARN
> > +	 * to avoid printing any information(not just a warning),
> > +	 * thus avoiding deadlocks. See commit 6b9dbedbe349 for
> > +	 * details.
> > +	 */
> >   	if (gfpflags & __GFP_NOWARN)
> > -		failslab.attr.no_warn = true;
> > +		flags |= FAULT_NOWARN;
> >   
> > -	return should_fail(&failslab.attr, s->object_size);
> > +	return should_fail_ex(&failslab.attr, s->object_size, flags);
> >   }
> >   
> >   static int __init setup_failslab(char *str)
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 7192ded44ad0..cb6fe715d983 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3902,6 +3902,8 @@ __setup("fail_page_alloc=", setup_fail_page_alloc);
> >   
> >   static bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
> >   {
> > +	int flags = 0;
> > +
> >   	if (order < fail_page_alloc.min_order)
> >   		return false;
> >   	if (gfp_mask & __GFP_NOFAIL)
> > @@ -3912,10 +3914,11 @@ static bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
> >   			(gfp_mask & __GFP_DIRECT_RECLAIM))
> >   		return false;
> >   
> > +	/* See comment in __should_failslab() */
> >   	if (gfp_mask & __GFP_NOWARN)
> > -		fail_page_alloc.attr.no_warn = true;
> > +		flags |= FAULT_NOWARN;
> >   
> > -	return should_fail(&fail_page_alloc.attr, 1 << order);
> > +	return should_fail_ex(&fail_page_alloc.attr, 1 << order, flags);
> >   }
> >   
> >   #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS

--
Thanks,
Qi