On Tue, Feb 24, 2015 at 07:19:24PM +0100, Michal Hocko wrote: > Tetsuo Handa has pointed out that __GFP_NOFAIL allocations might fail > after OOM killer is disabled if the allocation is performed by a > kernel thread. This behavior was introduced from the very beginning by > 7f33d49a2ed5 (mm, PM/Freezer: Disable OOM killer when tasks are frozen). > This means that the basic contract for the allocation request is broken > and the context requesting such an allocation might blow up unexpectedly. > > There are basically two ways forward. > 1) move oom_killer_disable after kernel threads are frozen. This has a > risk that the OOM victim wouldn't be able to finish because it would > depend on an already frozen kernel thread. This would be really > tricky to debug. > 2) do not fail GFP_NOFAIL allocation no matter what and risk a potential > Freezable kernel threads will loop and fail the suspend. Incidental > allocations after kernel threads are frozen will at least dump a > warning - if we are lucky and the serial console is still active of > course... > > This patch implements the later option because it is safer. We would see > warnings rather than allocation failures for the kernel threads which > would blow up otherwise and have a higher chances to identify > __GFP_NOFAIL users from deeper pm code. > > Signed-off-by: Michal Hocko <[email protected]> > --- > > We haven't seen any bug reports > > mm/oom_kill.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 642f38cb175a..ea8b443cd871 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -772,6 +772,10 @@ out: > schedule_timeout_killable(1); > } > > +static DEFINE_RATELIMIT_STATE(oom_disabled_rs, > + DEFAULT_RATELIMIT_INTERVAL, > + DEFAULT_RATELIMIT_BURST); > + > /** > * out_of_memory - tries to invoke OOM killer. > * @zonelist: zonelist pointer > @@ -792,6 +796,10 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t > gfp_mask, > if (!oom_killer_disabled) { > __out_of_memory(zonelist, gfp_mask, order, nodemask, > force_kill); > ret = true; > + } else if (gfp_mask & __GFP_NOFAIL) { > + if (__ratelimit(&oom_disabled_rs)) > + WARN(1, "Unable to make forward progress for > __GFP_NOFAIL because OOM killer is disbaled\n"); > + ret = true;
I'm fine with keeping the allocation looping, but is that message helpful? It seems completely useless to the user encountering it. Is it going to help kernel developers when we get a bug report with it? WARN_ON_ONCE()? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
