• Rusty Russell's avatar
    module: fix bne2 "gave up waiting for init of module libcrc32c" · 9bea7f23
    Rusty Russell authored
    Problem: it's hard to avoid an init routine stumbling over a
    request_module these days.  And it's not clear it's always a bad idea:
    for example, a module like kvm with dynamic dependencies on kvm-intel
    or kvm-amd would be neater if it could simply request_module the right
    one.
    
    In this particular case, it's libcrc32c:
    
    	libcrc32c_mod_init
    	 crypto_alloc_shash
    	  crypto_alloc_tfm
    	   crypto_find_alg
    	    crypto_alg_mod_lookup
    	     crypto_larval_lookup
    	      request_module
    
    If another module is waiting inside resolve_symbol() for libcrc32c to
    finish initializing (ie. bne2 depends on libcrc32c) then it does so
    holding the module lock, and our request_module() can't make progress
    until that is released.
    
    Waiting inside resolve_symbol() without the lock isn't all that hard:
    we just need to pass the -EBUSY up the call chain so we can sleep
    where we don't hold the lock.  Error reporting is a bit trickier: we
    need to copy the name of the unfinished module before releasing the
    lock.
    
    Other notes:
    1) This also fixes a theoretical issue where a weak dependency would allow
       symbol version mismatches to be ignored.
    2) We rename use_module to ref_module to make life easier for the only
       external user (the out-of-tree ksplice patches).
    Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Tim Abbot <tabbott@ksplice.com>
    Tested-by: default avatarBrandon Philips <bphilips@suse.de>
    9bea7f23
module.c 80.8 KB