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Re: [PATCH] zsmalloc: calling zs_map_object() from irq is a bug

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  Re: [PATCH] zsmalloc: calling zs_map_object() from irq is a bug Andrew Morton <akpm@linux-foundation.org> - 2017-09-27 02:30 +0200
    Re: [PATCH] zsmalloc: calling zs_map_object() from irq is a bug Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 02:50 +0200

#1740299 — Re: [PATCH] zsmalloc: calling zs_map_object() from irq is a bug

On Wed, 20 Sep 2017 15:47:39 +0900 Minchan Kim <minchan@kernel.org> wrote:

> On Wed, Sep 20, 2017 at 03:39:41PM +0900, Sergey Senozhatsky wrote:
> > Use BUG_ON(in_interrupt()) in zs_map_object(). Calling this
> > function from IRQ is a bug, because we use per-CPU mappings
> > and interrupt may corrupt those buffers.
> > 
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> 
> IMHO, corruption the buffer would be not enough to be a BUG_ON
> which stop the system fully so user loses any chances to shut
> down smooth/hunt it down.
> 
> More serious thing of our case is that it can leak other user's
> data by overwriting, which is more concern I am thinking now.
> 

In an off-list email Linus has basically stated that all new uses of
BUG_ON should include words in the changelog or code comments
explaining why it is justifiable to kill the machine when the condition
triggers.

So can we please have a v2 with the appropriate comment?

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#1741114

On (09/26/17 17:26), Andrew Morton wrote:
> > On Wed, Sep 20, 2017 at 03:39:41PM +0900, Sergey Senozhatsky wrote:
> > > Use BUG_ON(in_interrupt()) in zs_map_object(). Calling this
> > > function from IRQ is a bug, because we use per-CPU mappings
> > > and interrupt may corrupt those buffers.
> > > 
> > > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > 
> > IMHO, corruption the buffer would be not enough to be a BUG_ON
> > which stop the system fully so user loses any chances to shut
> > down smooth/hunt it down.
> > 
> > More serious thing of our case is that it can leak other user's
> > data by overwriting, which is more concern I am thinking now.
> > 
> 
> In an off-list email Linus has basically stated that all new uses of
> BUG_ON should include words in the changelog or code comments
> explaining why it is justifiable to kill the machine when the condition
> triggers.
> 
> So can we please have a v2 with the appropriate comment?

ah, OK. will follow up.

	-ss

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