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

From: Jeff Layton
Date: Mon May 06 2013 - 17:44:33 EST

Next message: Marc Dionne: "[PATCH] workqueue: Make schedule_work() available again to non GPL modules"
Previous message: Michal Marek: "Re: [PATCH] Fix cleaning in scripts/mod"
In reply to: Colin Cross: "Re: [PATCH 1/2] freezer: add unsafe versions of freezable helpers"
Next in thread: Colin Cross: "Re: [PATCH 1/2] freezer: add unsafe versions of freezable helpers"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On Mon, 6 May 2013 12:57:54 -0700
Colin Cross <ccross@xxxxxxxxxxx> wrote:

> On Mon, May 6, 2013 at 3:56 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> > On Fri, 3 May 2013 14:04:09 -0700
> > Colin Cross <ccross@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> >> ---
> >> 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.

It's pretty much all of the same VFS-level locks...

Basically, when a process wants to send a synchronous SMB to a CIFS
server, it'll send off the request and then call wait_for_response() to
wait on the reply. If you need a particular call stack, then you can
look in the rmdir() codepath as an example:

vfs_rmdir takes the i_mutex
cifs_rmdir (via the inode ops)
CIFSSMBRmDir (via the smb version ops)
SendReceive
wait_for_response

...at that point a freeze can occur while you're still holding the
i_mutex.

There are many other possibilities for other codepaths that end up in
wait_for_response(). Once we get a solution in place for NFS, we'll
need to do something very similar for CIFS.

--
Jeff Layton <jlayton@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Next message: Marc Dionne: "[PATCH] workqueue: Make schedule_work() available again to non GPL modules"
Previous message: Michal Marek: "Re: [PATCH] Fix cleaning in scripts/mod"
In reply to: Colin Cross: "Re: [PATCH 1/2] freezer: add unsafe versions of freezable helpers"
Next in thread: Colin Cross: "Re: [PATCH 1/2] freezer: add unsafe versions of freezable helpers"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]