linux-kernel - Re: [PATCH 2/6] rhashtable: remove incorrect comment on r{hl, hash}table_walk

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Date:   Mon, 23 Apr 2018 11:39:17 +1000
From:   NeilBrown <neilb@...e.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] rhashtable: remove incorrect comment on r{hl, hash}table_walk_enter()

On Thu, Apr 19 2018, Herbert Xu wrote:

> On Thu, Apr 19, 2018 at 08:56:28AM +1000, NeilBrown wrote:
>>
>> I don't want to do that - I just want the documentation to be correct
>> (or at least, not be blatantly incorrect).  The function does not sleep,
>> and is safe to call with spin locks held.
>> Do we need to spell out when it can be called?  If so, maybe:
>> 
>>    This function may be called from any process context, including
>>    non-preemptable context, but cannot be called from interrupts.
>
> Just to make it perfectly clear, how about "cannot be called from
> softirq or hardirq context"? Previously the not able to sleep part
> completely ruled out any ambiguity but the new wording could confuse
> people into thinking that this can be called from softirq context
> where it would be unsafe if mixed with process context usage.
>

Sound fair.  Could you Ack the following?  Then I'll resend all the
patches that have an ack.
I've realised that the "further improve stability of rhashtable_walk"
patch isn't actually complete, so I'll withdraw that for now.

Thanks,
NeilBrown

From e16c037398b6c057787437f3a0aaa7fd44c3bee3 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@...e.com>
Date: Mon, 16 Apr 2018 11:05:39 +1000
Subject: [PATCH] rhashtable: Revise incorrect comment on
 r{hl,hash}table_walk_enter()

Neither rhashtable_walk_enter() or rhltable_walk_enter() sleep, though
they do take a spinlock without irq protection.
So revise the comments to accurately state the contexts in which
these functions can be called.

Signed-off-by: NeilBrown <neilb@...e.com>
---
 include/linux/rhashtable.h | 5 +++--
 lib/rhashtable.c           | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 87d443a5b11d..4e1f535c2034 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -1268,8 +1268,9 @@ static inline int rhashtable_walk_init(struct rhashtable *ht,
  * For a completely stable walk you should construct your own data
  * structure outside the hash table.
  *
- * This function may sleep so you must not call it from interrupt
- * context or with spin locks held.
+ * This function may be called from any process context, including
+ * non-preemptable context, but cannot be called from softirq or
+ * hardirq context.
  *
  * You must call rhashtable_walk_exit after this function returns.
  */
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 2b2b79974b61..6d490f51174e 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -668,8 +668,9 @@ EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
  * For a completely stable walk you should construct your own data
  * structure outside the hash table.
  *
- * This function may sleep so you must not call it from interrupt
- * context or with spin locks held.
+ * This function may be called from any process context, including
+ * non-preemptable context, but cannot be called from softirq or
+ * hardirq context.
  *
  * You must call rhashtable_walk_exit after this function returns.
  */
-- 
2.14.0.rc0.dirty


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