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    8cc1df31
    netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING · 8cc1df31
    Zizhi Wo authored
    
    [ Upstream commit 22f9400a6f3560629478e0a64247b8fcc811a24d ]
    
    In fscache_create_volume(), there is a missing memory barrier between the
    bit-clearing operation and the wake-up operation. This may cause a
    situation where, after a wake-up, the bit-clearing operation hasn't been
    detected yet, leading to an indefinite wait. The triggering process is as
    follows:
    
      [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_wait
    
    In the above process, cookie1 and cookie2 has the same volume. When cookie1
    enters the -no_wait- process, it will clear the bit and wake up the waiting
    process. If a barrier is missing, it may cause cookie2 to remain in the
    -wait- process indefinitely.
    
    In commit 3288666c ("fscache: Use clear_and_wake_up_bit() in
    fscache_create_volume_work()"), barriers were added to similar operations
    in fscache_create_volume_work(), but fscache_create_volume() was missed.
    
    By combining the clear and wake operations into clear_and_wake_up_bit() to
    fix this issue.
    
    Fixes: bfa22da3 ("fscache: Provide and use cache methods to lookup/create/free a volume")
    Signed-off-by: default avatarZizhi Wo <wozizhi@huawei.com>
    Link: https://lore.kernel.org/r/20241107110649.3980193-6-wozizhi@huawei.com
    
    
    Acked-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
    8cc1df31
    History
    netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING
    Zizhi Wo authored
    
    [ Upstream commit 22f9400a6f3560629478e0a64247b8fcc811a24d ]
    
    In fscache_create_volume(), there is a missing memory barrier between the
    bit-clearing operation and the wake-up operation. This may cause a
    situation where, after a wake-up, the bit-clearing operation hasn't been
    detected yet, leading to an indefinite wait. The triggering process is as
    follows:
    
      [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_wait
    
    In the above process, cookie1 and cookie2 has the same volume. When cookie1
    enters the -no_wait- process, it will clear the bit and wake up the waiting
    process. If a barrier is missing, it may cause cookie2 to remain in the
    -wait- process indefinitely.
    
    In commit 3288666c ("fscache: Use clear_and_wake_up_bit() in
    fscache_create_volume_work()"), barriers were added to similar operations
    in fscache_create_volume_work(), but fscache_create_volume() was missed.
    
    By combining the clear and wake operations into clear_and_wake_up_bit() to
    fix this issue.
    
    Fixes: bfa22da3 ("fscache: Provide and use cache methods to lookup/create/free a volume")
    Signed-off-by: default avatarZizhi Wo <wozizhi@huawei.com>
    Link: https://lore.kernel.org/r/20241107110649.3980193-6-wozizhi@huawei.com
    
    
    Acked-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>