Messages in this thread Patch in this message | | | From | Adam Iwaniuk <> | Subject | [PATCH] sh: fix mmap_sem deadlock in sys_cacheflush | Date | Mon, 13 Oct 2014 13:59:12 +0200 |
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From: Adam Iwaniuk <adami@cubiware.com>
We can't be holding the mmap_sem while calling __flush_XXX_region/flush_icache_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_XXX_region/flush_icache_range and the fault, the down_read in do_page_fault will deadlock.
Signed-off-by: Adam Iwaniuk <adami@cubiware.com> --- arch/sh/kernel/sys_sh.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/sh/kernel/sys_sh.c b/arch/sh/kernel/sys_sh.c index 8c6a350..4aa294c 100644 --- a/arch/sh/kernel/sys_sh.c +++ b/arch/sh/kernel/sys_sh.c @@ -74,6 +74,7 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len, int op) up_read(¤t->mm->mmap_sem); return -EFAULT; } + up_read(¤t->mm->mmap_sem); switch (op & CACHEFLUSH_D_PURGE) { case CACHEFLUSH_D_INVAL: @@ -90,6 +91,5 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len, int op) if (op & CACHEFLUSH_I) flush_icache_range(addr, addr+len); - up_read(¤t->mm->mmap_sem); return 0; } -- 1.7.9.5
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