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Date: Mon, 6 May 2013 12:57:54 -0700
From: Colin Cross <ccross@...roid.com>
To: Jeff Layton <jlayton@...hat.com>
Cc: lkml <linux-kernel@...r.kernel.org>,
Trond Myklebust <Trond.Myklebust@...app.com>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
"David S. Miller" <davem@...emloft.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Mandeep Singh Baines <msb@...omium.org>,
Paul Walmsley <paul@...an.com>,
Al Viro <viro@...iv.linux.org.uk>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Oleg Nesterov <oleg@...hat.com>,
linux-nfs <linux-nfs@...r.kernel.org>,
Linux PM list <linux-pm@...r.kernel.org>,
netdev <netdev@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Tejun Heo <tj@...nel.org>, Ben Chan <benchan@...omium.org>,
smfrench@...il.com
Subject: Re: [PATCH 1/2] freezer: add unsafe versions of freezable helpers
On Mon, May 6, 2013 at 3:56 AM, Jeff Layton <jlayton@...hat.com> wrote:
> On Fri, 3 May 2013 14:04:09 -0700
> Colin Cross <ccross@...roid.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@...roid.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.
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