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    SubjectRe: [BUGFIX] memcg: fix res_counter_read_u64 lock aware (Was Re: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory()
    On Wed, 26 Jan 2011 17:08:24 -0800
    Andrew Morton <akpm@linux-foundation.org> wrote:

    > On Thu, 27 Jan 2011 09:53:42 +0900
    > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    >
    > > res_counter_read_u64 reads u64 value without lock. It's dangerous
    > > in 32bit environment. This patch adds lock.
    > >
    > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > ---
    > > include/linux/res_counter.h | 13 ++++++++++++-
    > > kernel/res_counter.c | 2 +-
    > > 2 files changed, 13 insertions(+), 2 deletions(-)
    > >
    > > Index: mmotm-0125/include/linux/res_counter.h
    > > ===================================================================
    > > --- mmotm-0125.orig/include/linux/res_counter.h
    > > +++ mmotm-0125/include/linux/res_counter.h
    > > @@ -68,7 +68,18 @@ struct res_counter {
    > > * @pos: and the offset.
    > > */
    > >
    > > -u64 res_counter_read_u64(struct res_counter *counter, int member);
    > > +u64 res_counter_read_u64_locked(struct res_counter *counter, int member);
    > > +
    > > +static inline u64 res_counter_read_u64(struct res_counter *counter, int member)
    > > +{
    > > + unsigned long flags;
    > > + u64 ret;
    > > +
    > > + spin_lock_irqsave(&counter->lock, flags);
    > > + ret = res_counter_read_u64_locked(counter, member);
    > > + spin_unlock_irqrestore(&counter->lock, flags);
    > > + return ret;
    > > +}
    > >
    > > ssize_t res_counter_read(struct res_counter *counter, int member,
    > > const char __user *buf, size_t nbytes, loff_t *pos,
    > > Index: mmotm-0125/kernel/res_counter.c
    > > ===================================================================
    > > --- mmotm-0125.orig/kernel/res_counter.c
    > > +++ mmotm-0125/kernel/res_counter.c
    > > @@ -126,7 +126,7 @@ ssize_t res_counter_read(struct res_coun
    > > pos, buf, s - buf);
    > > }
    > >
    > > -u64 res_counter_read_u64(struct res_counter *counter, int member)
    > > +u64 res_counter_read_u64_locked(struct res_counter *counter, int member)
    > > {
    > > return *res_counter_member(counter, member);
    > > }
    >
    > We don't need the lock on 64-bit platforms!
    >
    All res_counter function doesn't handle 32/64 bit differences. So, I did
    in this style for now.

    > And there's zero benefit to inlining the spin_lock/unlock(), given that
    > the function will always be making a function call anyway.
    >
    Ok.

    > See i_size_read() for inspiration.
    >

    I hate res_counter ;) I'll update patch.

    Thanks,
    -Kame





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