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

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

On 2022/11/8 17:32, Wei Yongjun wrote:
> On 2022/11/8 16:58, Qi Zheng wrote:
> > 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?
>
> Yes, just like:
>
> echo 1 > /sys/kernel/debug/failslab/no_warn  #disable message
> echo 0 > /sys/kernel/debug/failslab/no_warn  #enable message

Got it. Let's wait for the other people's comments and suggestions. :)

> Regards
> Wei Yongjun
>
> > 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