On Thu, Apr 13, 2017 at 12:29:25AM +0200, Borislav Petkov wrote: > On Wed, Apr 12, 2017 at 03:26:19PM -0700, Luck, Tony wrote: > > We can futz with that and have them specify which chain (or both) > > that they want to be added to. > > Well, I didn't want the atomic chain to be a notifier because we can > keep it simple and non-blocking. Only the process context one will be. > > So the question is, do we even have a use case for outside consumers > hanging on the atomic chain? Because if not, we're good to go.
Ok, new day, new patch. Below is what we could do: we don't call the notifier at all on the atomic path but only print the MCEs. We do log them and if the machine survives, we process them accordingly. This is only a fix for upstream so that the current issue at hand is addressed. For later, we'd need to split the paths in: critical_print_mce() or somesuch which immediately dumps the MCE to dmesg, and mce_log() which does the slow path of logging MCEs and calling the blocking notifier. Now, I'd want to have decoding of the MCE on the critical path too so I have to think about how to do that nicely. Maybe move the decoding bits which are the same between Intel and AMD in mce.c and have some vendor-specific, fast calls. We'll see. Btw, this is something Ingo has been mentioning for a while. Anyway, here's just the urgent fix for now. Thanks. --- From: Vishal Verma <[email protected]> Date: Tue, 11 Apr 2017 16:44:57 -0600 Subject: [PATCH] x86/mce: Make the MCE notifier a blocking one The NFIT MCE handler callback (for handling media errors on NVDIMMs) takes a mutex to add the location of a memory error to a list. But since the notifier call chain for machine checks (x86_mce_decoder_chain) is atomic, we get a lockdep splat like: BUG: sleeping function called from invalid context at kernel/locking/mutex.c:620 in_atomic(): 1, irqs_disabled(): 0, pid: 4, name: kworker/0:0 [..] Call Trace: dump_stack ___might_sleep __might_sleep mutex_lock_nested ? __lock_acquire nfit_handle_mce notifier_call_chain atomic_notifier_call_chain ? atomic_notifier_call_chain mce_gen_pool_process Convert the notifier to a blocking one which gets to run only in process context. Boris: remove the notifier call in atomic context in print_mce(). For now, let's print the MCE on the atomic path so that we can make sure it goes out. We still log it for process context later. Reported-by: Ross Zwisler <[email protected]> Signed-off-by: Vishal Verma <[email protected]> Cc: Tony Luck <[email protected]> Cc: Dan Williams <[email protected]> Cc: linux-edac <[email protected]> Cc: x86-ml <[email protected]> Cc: <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Fixes: 6839a6d96f4e ("nfit: do an ARS scrub on hitting a latent media error") Signed-off-by: Borislav Petkov <[email protected]> --- arch/x86/kernel/cpu/mcheck/mce-genpool.c | 2 +- arch/x86/kernel/cpu/mcheck/mce-internal.h | 2 +- arch/x86/kernel/cpu/mcheck/mce.c | 18 ++++-------------- 3 files changed, 6 insertions(+), 16 deletions(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce-genpool.c b/arch/x86/kernel/cpu/mcheck/mce-genpool.c index 1e5a50c11d3c..217cd4449bc9 100644 --- a/arch/x86/kernel/cpu/mcheck/mce-genpool.c +++ b/arch/x86/kernel/cpu/mcheck/mce-genpool.c @@ -85,7 +85,7 @@ void mce_gen_pool_process(struct work_struct *__unused) head = llist_reverse_order(head); llist_for_each_entry_safe(node, tmp, head, llnode) { mce = &node->mce; - atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce); + blocking_notifier_call_chain(&x86_mce_decoder_chain, 0, mce); gen_pool_free(mce_evt_pool, (unsigned long)node, sizeof(*node)); } } diff --git a/arch/x86/kernel/cpu/mcheck/mce-internal.h b/arch/x86/kernel/cpu/mcheck/mce-internal.h index 903043e6a62b..19592ba1a320 100644 --- a/arch/x86/kernel/cpu/mcheck/mce-internal.h +++ b/arch/x86/kernel/cpu/mcheck/mce-internal.h @@ -13,7 +13,7 @@ enum severity_level { MCE_PANIC_SEVERITY, }; -extern struct atomic_notifier_head x86_mce_decoder_chain; +extern struct blocking_notifier_head x86_mce_decoder_chain; #define ATTR_LEN 16 #define INITIAL_CHECK_INTERVAL 5 * 60 /* 5 minutes */ diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 5accfbdee3f0..8e470735b16b 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -123,7 +123,7 @@ static void (*quirk_no_way_out)(int bank, struct mce *m, struct pt_regs *regs); * CPU/chipset specific EDAC code can register a notifier call here to print * MCE errors in a human-readable form. */ -ATOMIC_NOTIFIER_HEAD(x86_mce_decoder_chain); +BLOCKING_NOTIFIER_HEAD(x86_mce_decoder_chain); /* Do initial initialization of a struct mce */ void mce_setup(struct mce *m) @@ -220,7 +220,7 @@ void mce_register_decode_chain(struct notifier_block *nb) WARN_ON(nb->priority > MCE_PRIO_LOWEST && nb->priority < MCE_PRIO_EDAC); - atomic_notifier_chain_register(&x86_mce_decoder_chain, nb); + blocking_notifier_chain_register(&x86_mce_decoder_chain, nb); } EXPORT_SYMBOL_GPL(mce_register_decode_chain); @@ -228,7 +228,7 @@ void mce_unregister_decode_chain(struct notifier_block *nb) { atomic_dec(&num_notifiers); - atomic_notifier_chain_unregister(&x86_mce_decoder_chain, nb); + blocking_notifier_chain_unregister(&x86_mce_decoder_chain, nb); } EXPORT_SYMBOL_GPL(mce_unregister_decode_chain); @@ -321,18 +321,8 @@ static void __print_mce(struct mce *m) static void print_mce(struct mce *m) { - int ret = 0; - __print_mce(m); - - /* - * Print out human-readable details about the MCE error, - * (if the CPU has an implementation for that) - */ - ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m); - if (ret == NOTIFY_STOP) - return; - + mce_log(m); pr_emerg_ratelimited(HW_ERR "Run the above through 'mcelog --ascii'\n"); } -- 2.11.0 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
