linux-kernel - Re: [PATCH 05/10] uprobes: share the i_mmap

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Message-ID: <20141027070329.GA10867@linux.vnet.ibm.com>
Date:	Mon, 27 Oct 2014 12:33:29 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Davidlohr Bueso <dave@...olabs.net>,
	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, hughd@...gle.com, riel@...hat.com,
	mgorman@...e.de, peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, dbueso@...e.de, linux-mm@...ck.org
Subject: Re: [PATCH 05/10] uprobes: share the i_mmap_rwsem

* Davidlohr Bueso <dave@...olabs.net> [2014-10-24 15:06:15]:

> Both register and unregister call build_map_info() in order
> to create the list of mappings before installing or removing
> breakpoints for every mm which maps file backed memory. As
> such, there is no reason to hold the i_mmap_rwsem exclusively,
> so share it and allow concurrent readers to build the mapping
> data.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>


Copying Oleg (since he should have been copied on this one)

Please see one comment below.

Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com> 

> ---
>  kernel/events/uprobes.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 045b649..7a9e620 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -724,7 +724,7 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
>  	int more = 0;
>  
>   again:
> -	i_mmap_lock_write(mapping);
> +	i_mmap_lock_read(mapping);
>  	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
>  		if (!valid_vma(vma, is_register))
>  			continue;


Just after this, we have
if (!prev && !more) {
	/*
	 * Needs GFP_NOWAIT to avoid i_mmap_mutex recursion through
	 * reclaim. This is optimistic, no harm done if it fails.
	 */
	prev = kmalloc(sizeof(struct map_info),
			GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
	if (prev)
		prev->next = NULL;
}

However in patch 02/10
I dont think the comment referring to i_mmap_mutex was modified to
refer i_mmap_lock_write.

When thats taken care off, this patch should change that part accordingly.


-- 
Thanks and Regards
Srikar Dronamraju

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