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Subject[PATCH] sh: fix mmap_sem deadlock in sys_cacheflush
Date
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(&current->mm->mmap_sem);
return -EFAULT;
}
+ up_read(&current->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(&current->mm->mmap_sem);
return 0;
}
--
1.7.9.5


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