Re: [PATCH 1/2] freezer: add unsafe versions of freezable helpers

[Colin Cross <ccross@android.com>]

On Mon, May 6, 2013 at 3:56 AM, Jeff Layton <jlayton@redhat.com> wrote:
> On Fri,  3 May 2013 14:04:09 -0700
> Colin Cross <ccross@android.com> wrote:
>
>> NFS calls the freezable helpers with locks held, which is unsafe
>> and caused lockdep warnings when 6aa9707 "lockdep: check that no
>> locks held at freeze time" was applied (reverted in dbf520a).
>> Add new *_unsafe versions of the helpers that will not run the
>> lockdep test when 6aa9707 is reapplied, and call them from NFS.
>>
>> Signed-off-by: Colin Cross <ccross@android.com>
>> ---
>>  fs/nfs/inode.c          |  2 +-
>>  fs/nfs/nfs3proc.c       |  2 +-
>>  fs/nfs/nfs4proc.c       |  4 ++--
>>  include/linux/freezer.h | 42 +++++++++++++++++++++++++++++++++++++++++-
>>  net/sunrpc/sched.c      |  2 +-
>>  5 files changed, 46 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
>> index 1f94167..53cbee5 100644
>> --- a/fs/nfs/inode.c
>> +++ b/fs/nfs/inode.c
>> @@ -79,7 +79,7 @@ int nfs_wait_bit_killable(void *word)
>>  {
>>       if (fatal_signal_pending(current))
>>               return -ERESTARTSYS;
>> -     freezable_schedule();
>> +     freezable_schedule_unsafe();
>>       return 0;
>>  }
>>  EXPORT_SYMBOL_GPL(nfs_wait_bit_killable);
>> diff --git a/fs/nfs/nfs3proc.c b/fs/nfs/nfs3proc.c
>> index 43ea96c..ce90eb4 100644
>> --- a/fs/nfs/nfs3proc.c
>> +++ b/fs/nfs/nfs3proc.c
>> @@ -33,7 +33,7 @@ nfs3_rpc_wrapper(struct rpc_clnt *clnt, struct rpc_message *msg, int flags)
>>               res = rpc_call_sync(clnt, msg, flags);
>>               if (res != -EJUKEBOX)
>>                       break;
>> -             freezable_schedule_timeout_killable(NFS_JUKEBOX_RETRY_TIME);
>> +             freezable_schedule_timeout_killable_unsafe(NFS_JUKEBOX_RETRY_TIME);
>>               res = -ERESTARTSYS;
>>       } while (!fatal_signal_pending(current));
>>       return res;
>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>> index 0ad025e..a236077 100644
>> --- a/fs/nfs/nfs4proc.c
>> +++ b/fs/nfs/nfs4proc.c
>> @@ -266,7 +266,7 @@ static int nfs4_delay(struct rpc_clnt *clnt, long *timeout)
>>               *timeout = NFS4_POLL_RETRY_MIN;
>>       if (*timeout > NFS4_POLL_RETRY_MAX)
>>               *timeout = NFS4_POLL_RETRY_MAX;
>> -     freezable_schedule_timeout_killable(*timeout);
>> +     freezable_schedule_timeout_killable_unsafe(*timeout);
>>       if (fatal_signal_pending(current))
>>               res = -ERESTARTSYS;
>>       *timeout <<= 1;
>> @@ -4309,7 +4309,7 @@ int nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4
>>  static unsigned long
>>  nfs4_set_lock_task_retry(unsigned long timeout)
>>  {
>> -     freezable_schedule_timeout_killable(timeout);
>> +     freezable_schedule_timeout_killable_unsafe(timeout);
>>       timeout <<= 1;
>>       if (timeout > NFS4_LOCK_MAXTIMEOUT)
>>               return NFS4_LOCK_MAXTIMEOUT;
>> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
>> index e70df40..5b31e21c 100644
>> --- a/include/linux/freezer.h
>> +++ b/include/linux/freezer.h
>> @@ -46,7 +46,11 @@ extern int freeze_kernel_threads(void);
>>  extern void thaw_processes(void);
>>  extern void thaw_kernel_threads(void);
>>
>> -static inline bool try_to_freeze(void)
>> +/*
>> + * DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION
>> + * If try_to_freeze causes a lockdep warning it means the caller may deadlock
>> + */
>> +static inline bool try_to_freeze_unsafe(void)
>>  {
>>       might_sleep();
>>       if (likely(!freezing(current)))
>> @@ -54,6 +58,11 @@ static inline bool try_to_freeze(void)
>>       return __refrigerator(false);
>>  }
>>
>> +static inline bool try_to_freeze(void)
>> +{
>> +     return try_to_freeze_unsafe();
>> +}
>> +
>>  extern bool freeze_task(struct task_struct *p);
>>  extern bool set_freezable(void);
>>
>> @@ -115,6 +124,14 @@ static inline void freezer_count(void)
>>       try_to_freeze();
>>  }
>>
>> +/* DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION */
>> +static inline void freezer_count_unsafe(void)
>> +{
>> +     current->flags &= ~PF_FREEZER_SKIP;
>> +     smp_mb();
>> +     try_to_freeze_unsafe();
>> +}
>> +
>>  /**
>>   * freezer_should_skip - whether to skip a task when determining frozen
>>   *                    state is reached
>> @@ -152,6 +169,14 @@ static inline bool freezer_should_skip(struct task_struct *p)
>>       freezer_count();                                                \
>>  })
>>
>> +/* DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION */
>> +#define freezable_schedule_unsafe()                                  \
>> +({                                                                   \
>> +     freezer_do_not_count();                                         \
>> +     schedule();                                                     \
>> +     freezer_count_unsafe();                                         \
>> +})
>> +
>>  /* Like schedule_timeout_killable(), but should not block the freezer. */
>>  #define freezable_schedule_timeout_killable(timeout)                 \
>>  ({                                                                   \
>> @@ -162,6 +187,16 @@ static inline bool freezer_should_skip(struct task_struct *p)
>>       __retval;                                                       \
>>  })
>>
>> +/* DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION */
>> +#define freezable_schedule_timeout_killable_unsafe(timeout)          \
>> +({                                                                   \
>> +     long __retval;                                                  \
>> +     freezer_do_not_count();                                         \
>> +     __retval = schedule_timeout_killable(timeout);                  \
>> +     freezer_count_unsafe();                                         \
>> +     __retval;                                                       \
>> +})
>> +
>>  /*
>>   * Freezer-friendly wrappers around wait_event_interruptible(),
>>   * wait_event_killable() and wait_event_interruptible_timeout(), originally
>> @@ -225,9 +260,14 @@ static inline void set_freezable(void) {}
>>
>>  #define freezable_schedule()  schedule()
>>
>> +#define freezable_schedule_unsafe()  schedule()
>> +
>>  #define freezable_schedule_timeout_killable(timeout)                 \
>>       schedule_timeout_killable(timeout)
>>
>> +#define freezable_schedule_timeout_killable_unsafe(timeout)          \
>> +     schedule_timeout_killable(timeout)
>> +
>>  #define wait_event_freezable(wq, condition)                          \
>>               wait_event_interruptible(wq, condition)
>>
>> diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
>> index f8529fc..8dcfadc 100644
>> --- a/net/sunrpc/sched.c
>> +++ b/net/sunrpc/sched.c
>> @@ -254,7 +254,7 @@ static int rpc_wait_bit_killable(void *word)
>>  {
>>       if (fatal_signal_pending(current))
>>               return -ERESTARTSYS;
>> -     freezable_schedule();
>> +     freezable_schedule_unsafe();
>>       return 0;
>>  }
>>
>
> Looks reasonable, but note that CIFS uses wait_event_freezekillable
> with locks held too, which will likely have the same problem and will
> need the same workaround for now.

I didn't see any lockdep warnings reported on the mailing list when
the lockdep patch was previously applied, can you point me to the lock
that is held when wait_event_freezkillable is called?  I don't want to
add an _unsafe call where its not needed and cause more confusion.