In the Linux kernel, the following vulnerability has been resolved:netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATINGIn fscache_create_volume(), there is a missing memory barrier between thebit-clearing operation and the wake-up operation. This may cause asituation where, after a wake-up, the bit-clearing operation hasn't beendetected yet, leading to an indefinite wait. The triggering process is asfollows: [cookie1] [cookie2] [volume_work]fscache_perform_lookup fscache_create_volume fscache_perform_lookup fscache_create_volume fscache_create_volume_work cachefiles_acquire_volume clear_and_wake_up_bit test_and_set_bit test_and_set_bit goto maybe_wait goto no_waitIn the above process, cookie1 and cookie2 has the same volume. When cookie1enters the -no_wait- process, it will clear the bit and wake up the waitingprocess. If a barrier is missing, it may cause cookie2 to remain in the-wait- process indefinitely.In commit 3288666c7256 ("fscache: Use clear_and_wake_up_bit() infscache_create_volume_work()"), barriers were added to similar operationsin fscache_create_volume_work(), but fscache_create_volume() was missed.By combining the clear and wake operations into clear_and_wake_up_bit() tofix this issue.
