From mboxrd@z Thu Jan 1 00:00:00 1970 From: john.stultz@linaro.org (John Stultz) Date: Mon, 13 Dec 2010 20:57:39 -0800 Subject: [PATCH 4/4] Do not call flush_cache_user_range with mmap_sem held In-Reply-To: <1292302659-1863-1-git-send-email-john.stultz@linaro.org> References: <1292302659-1863-1-git-send-email-john.stultz@linaro.org> Message-ID: <1292302659-1863-5-git-send-email-john.stultz@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Dima Zavin We can't be holding the mmap_sem while calling flush_cache_user_range because the flush can fault. If we fault on a user address, the page fault handler will try to take mmap_sem again. Since both places acquire the read lock, most of the time it succeeds. However, if another thread tries to acquire the write lock on the mmap_sem (e.g. mmap) in between the call to flush_cache_user_range and the fault, the down_read in do_page_fault will deadlock. Also, since we really can't be holding the mmap_sem while calling flush_cache_user_range AND vma is actually unused by the flush itself, get rid of vma as an argument. CC: Nicolas Pitre CC: Russell King Signed-off-by: Dima Zavin Signed-off-by: John Stultz --- arch/arm/include/asm/cacheflush.h | 2 +- arch/arm/kernel/traps.c | 4 +++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h index 3acd8fa..f533a6a 100644 --- a/arch/arm/include/asm/cacheflush.h +++ b/arch/arm/include/asm/cacheflush.h @@ -377,7 +377,7 @@ extern void flush_cache_page(struct vm_area_struct *vma, unsigned long user_addr * Harvard caches are synchronised for the user space address range. * This is used for the ARM private sys_cacheflush system call. */ -#define flush_cache_user_range(vma,start,end) \ +#define flush_cache_user_range(start,end) \ __cpuc_coherent_user_range((start) & PAGE_MASK, PAGE_ALIGN(end)) /* diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c index 446aee9..7644a56 100644 --- a/arch/arm/kernel/traps.c +++ b/arch/arm/kernel/traps.c @@ -451,7 +451,9 @@ do_cache_op(unsigned long start, unsigned long end, int flags) if (end > vma->vm_end) end = vma->vm_end; - flush_cache_user_range(vma, start, end); + up_read(&mm->mmap_sem); + flush_cache_user_range(start, end); + return; } up_read(&mm->mmap_sem); } -- 1.7.3.2.146.gca209