On Wed, Feb 25, 2015 at 1:09 AM, Konstantin Khlebnikov <[email protected]> wrote: > 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.
Ah, that's used in freeze/suspend code. I thought that some kind of sysctl for brave sysadmins. > >> >> -- >> 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/
