Re: [PATCH] mm: Downgrade mmap_sem before locking or populating on mmap
From: Andy Lutomirski <luto@amacapital.net>
Date: 2012-12-14 16:13:08
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On Fri, Dec 14, 2012 at 6:49 AM, Al Viro [off-list ref] wrote:
On Fri, Dec 14, 2012 at 03:14:50AM -0800, Andy Lutomirski wrote:quoted
quoted
Wait a minute. get_user_pages() relies on ->mmap_sem being held. Unless I'm seriously misreading your patch it removes that protection. And yes, I'm aware of execve-related exception; it's in special circumstances - bprm->mm is guaranteed to be not shared (and we need to rearchitect that area anyway, but that's a separate story).Unless I completely screwed up the patch, ->mmap_sem is still held for read (it's downgraded from write). It's just not held for write anymore.Huh? I'm talking about the call of get_user_pages() in aio_setup_ring(). With your patch it's done completely outside of ->mmap_sem, isn't it?
Oh, /that/ call to get_user_pages. That would qualify as screwing up... Since dropping and reacquiring mmap_sem there is probably a bad idea there, I'll rework this and post a v2. --Andy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>