Re: [PATCH] Lockdep treats down_write_trylock like regular down_write

Pavel Emelianov wrote:

This causes constructions like

down_write(&mm1->mmap_sem);
if (down_write_trylock(&mm2->mmap_sem)) {
       ...
       up_write(&mm2->mmap_sem);
}
up_write(&mm1->mmap_sem);

generate a lockdep warning about circular locking dependence.

please show me why this is safe, especially if you intermix it with down_read()'s... like copy_to_user and co may do.

this feels like a very unsafe construct to me...
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