On Tue, Feb 24, 2015 at 10:11 PM, Johannes Weiner <[email protected]> wrote: > 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()?
maybe panic() ? If somebody turns off oom-killer it seems he's pretty sure that he has enough memory. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to [email protected]. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"[email protected]";> [email protected] </a> -- 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/
