Messages in this thread Patch in this message | | | Date | Mon, 2 Jun 2008 14:31:36 -0700 | From | Suresh Siddha <> | Subject | Re: CONFIG_PREEMPT causes corruption of application's FPU stack |
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On Sun, Jun 01, 2008 at 07:11:02PM +0200, Simon Holm Thøgersen wrote: > søn, 01 06 2008 kl. 11:01 +0200, skrev j.mell@t-online.de: > [...] > > > > 3. If I revert the patch > > > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=acc207616a91a413a50fdd8847a747c4a7324167 > > > > in 2.6.20, Einstein does not crash anymore (program was run for more than > > 30 hours while system was in normal use with programming, multi-media > > etc.). Unfortunately git refuses to revert this patch in 2.6.26-rc4. > [...] > > I don't think the bisected commit is responsible for anything, but > triggering a bug elsewhere with your workload. I've been chasing the > same problem I think, but with other symptoms.
Simon, There seems to be multiple issues here. fpu corruption seems to be a different problem compared to the issue you have encountered.
> > I'm triggering the following by running an lguest guest, but I guess the > workload just need to have the right scheduler intensity to trigger the > bug. > > BUG: sleeping function called from invalid context at mm/slab.c:3052 > in_atomic():1, irqs_disabled():0 > Pid: 4771, comm: lguest Not tainted > 2.6.26-rc4-debug-only-preemptible-00103-g1beee8d #3 > [<c01146ee>] __might_sleep+0xe4/0xeb > [<c01605d9>] kmem_cache_alloc+0x22/0xb4 > [<c0108479>] init_fpu+0xb0/0x14d > [<c0104768>] math_state_restore+0x26/0x5d > [<c01045ab>] device_not_available+0x43/0x48 > [<c011007b>] ? handle_vm86_fault+0x213/0x6b8 > [<c01029ad>] ? __switch_to+0x23/0x113 > [<c02d6c9f>] schedule+0x221/0x2a4
Simon, Can you please try the appended patch and see if it fixes this issue? Thanks. ---
[patch] x86: fix blocking call (math_state_restore()) condition in __switch_to
Add tsk_used_math() checks to prevent calling math_state_restore() which can sleep in the case of !tsk_used_math(). This prevents making a blocking call in __switch_to().
Apparently "fpu_counter > 5" check is not enough, as in some signal handling and fork/exec scenarios, fpu_counter > 5 and !tsk_used_math() is possible.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> ---
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index f8476df..6d54833 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -649,8 +649,11 @@ struct task_struct * __switch_to(struct task_struct *prev_p, struct task_struct /* If the task has used fpu the last 5 timeslices, just do a full * restore of the math state immediately to avoid the trap; the * chances of needing FPU soon are obviously high now + * + * tsk_used_math() checks prevent calling math_state_restore(), + * which can sleep in the case of !tsk_used_math() */ - if (next_p->fpu_counter > 5) + if (tsk_used_math(next_p) && next_p->fpu_counter > 5) math_state_restore(); /* diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index e2319f3..ac54ff5 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -658,8 +658,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) /* If the task has used fpu the last 5 timeslices, just do a full * restore of the math state immediately to avoid the trap; the * chances of needing FPU soon are obviously high now + * + * tsk_used_math() checks prevent calling math_state_restore(), + * which can sleep in the case of !tsk_used_math() */ - if (next_p->fpu_counter>5) + if (tsk_used_math(next_p) && next_p->fpu_counter > 5) math_state_restore(); return prev_p; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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