linux-kernel - Ask for help on the memory allocation for process shared mutex (resend with plain text)

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Message-ID: <CAGO-9moQrepikUk198XjgiE=hC2W6u_Wsup8yK=ooBfPNg1PfQ@mail.gmail.com>
Date:	Fri, 30 May 2014 10:57:08 +0800
From:	yang ben <benyangfsl@...il.com>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Ask for help on the memory allocation for process shared mutex
 (resend with plain text)

Dear experts,

I came across a memory/mutex issue. Would you kindly shed some light on it?

I use pthread_mutex_xxx API to protect processes in user space. Since
it should be process shared, I allocated a shared memory to store
pthread_mutex_t structure.

The shared memory is allocated using vmalloc_user() and mapped using
remap_vmalloc_range() in driver. However, get_futex_key() will always
return -EFAULT, because page_head->mapping==0.

futex.c (Linux-3.10.31)
         if (!page_head->mapping) {
                 int shmem_swizzled = PageSwapCache(page_head);
                 unlock_page(page_head);
                 put_page(page_head);
                 if (shmem_swizzled)
                         goto again;
                 return -EFAULT;
         }

Is there special requirement on the memory to store mutex? What's the
correct way to allocate such memory in driver?
Thanks in advance!

Regards,
Ben
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