Messages in this thread Patch in this message | | | Date | Sun, 19 Jan 2014 12:02:22 -0700 (MST) | From | Nate Eldredge <> | Subject | Re: math_state_restore and kernel_fpu_end disable interrupts? |
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[Here's my original message, since George's reply didn't quote or reference it: https://lkml.org/lkml/2014/1/18/3. Summary: math_state_restore() always leaves interrupts disabled, and I think this is a bug.]
On Sun, 19 Jan 2014, George Spelvin wrote:
> THANK YOU! > > I've been having a problem with ext4 metadata checksums, which use SSE > for large blocks, and traced it to kernel_fpu_end() disabling interrupts, > but had paused to debug this (I assumed well-tested) piece of kernel > code before pushing it harder.
Interesting. I guess it's not surprising this has other effects.
Here's the commit that added the code in question (about 6 years ago): https://github.com/torvalds/linux/commit/aa283f49276e7d840a40fb01eee6de97eaa7e012
It's credited to Suresh Siddha, whom I've cc'ed (along with others who signed off). Suresh, if you're still around, could you comment on why math_state_restore always leaves interrupts disabled, regardless of their state on entry? Is there a deep reason or is it a bug?
Assuming it's a bug, here's the obvious patch:
--- linux-source-3.11.0/arch/x86/kernel/traps.c 2013-09-02 14:46:10.000000000 -0600 +++ linux-source-3.11.0-nate/arch/x86/kernel/traps.c 2014-01-19 11:25:32.977221476 -0700 @@ -624,6 +624,9 @@ struct task_struct *tsk = current;
if (!tsk_used_math(tsk)) { + unsigned long flags; + + local_save_flags(flags); local_irq_enable(); /* * does a slab alloc which can sleep @@ -635,7 +638,7 @@ do_group_exit(SIGKILL); return; } - local_irq_disable(); + local_irq_restore(flags); }
__thread_fpu_begin(tsk); I tested it briefly: the kernel still boots fine, and it fixes the problem I was seeing (BUG() when core dumping on ecryptfs). George, does it help your problem?
Thanks everyone!
> (Search October-December LKML archives for "3.11.4: kernel BUG at > fs/buffer.c:1268".")
-- Nate Eldredge nate@thatsmathematics.com
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