[PATCH] sched/wait: Fix the signal handling fix

[PATCH] sched/wait: Fix the signal handling fix

[Peter Zijlstra]

Jan Stancek reported that I wrecked things for him by fixing things for
Vladimir :/

His report was due to an UNINTERRUPTIBLE wait getting -EINTR, which
should not be possible, however my previous patch made this possible by
unconditionally checking signal_pending().

We cannot use current->state as was done previously, because the
instruction after the store to that variable it can be changed. We must
instead pass the initial state along and use that.

Fixes: 68985633bccb ("sched/wait: Fix signal handling in bit wait helpers")
Reported-by: Jan Stancek <jstancek@redhat.com>
Reported-by: Chris Mason <clm@fb.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com>
Tested-by: Chris Mason <clm@fb.com>
Reviewed-by: Paul Turner <pjt@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: tglx@linutronix.de
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: hpa@zytor.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 fs/cifs/inode.c      |    6 +++---
 fs/nfs/inode.c       |    6 +++---
 fs/nfs/internal.h    |    2 +-
 fs/nfs/pagelist.c    |    2 +-
 fs/nfs/pnfs.c        |    4 ++--
 include/linux/wait.h |   10 +++++-----
 kernel/sched/wait.c  |   20 ++++++++++----------
 net/sunrpc/sched.c   |    6 +++---
 8 files changed, 28 insertions(+), 28 deletions(-)

--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -1831,11 +1831,11 @@ cifs_invalidate_mapping(struct inode *in
  * @word: long word containing the bit lock
  */
 static int
-cifs_wait_bit_killable(struct wait_bit_key *key)
+cifs_wait_bit_killable(struct wait_bit_key *key, int mode)
 {
-	if (fatal_signal_pending(current))
-		return -ERESTARTSYS;
 	freezable_schedule_unsafe();
+	if (signal_pending_state(mode, current))
+		return -ERESTARTSYS;
 	return 0;
 }
 
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -75,11 +75,11 @@ nfs_fattr_to_ino_t(struct nfs_fattr *fat
  * nfs_wait_bit_killable - helper for functions that are sleeping on bit locks
  * @word: long word containing the bit lock
  */
-int nfs_wait_bit_killable(struct wait_bit_key *key)
+int nfs_wait_bit_killable(struct wait_bit_key *key, int mode)
 {
-	if (fatal_signal_pending(current))
-		return -ERESTARTSYS;
 	freezable_schedule_unsafe();
+	if (signal_pending_state(mode, current))
+		return -ERESTARTSYS;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(nfs_wait_bit_killable);
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -379,7 +379,7 @@ extern int nfs_drop_inode(struct inode *
 extern void nfs_clear_inode(struct inode *);
 extern void nfs_evict_inode(struct inode *);
 void nfs_zap_acl_cache(struct inode *inode);
-extern int nfs_wait_bit_killable(struct wait_bit_key *key);
+extern int nfs_wait_bit_killable(struct wait_bit_key *key, int mode);
 
 /* super.c */
 extern const struct super_operations nfs_sops;
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -129,7 +129,7 @@ __nfs_iocounter_wait(struct nfs_io_count
 		set_bit(NFS_IO_INPROGRESS, &c->flags);
 		if (atomic_read(&c->io_count) == 0)
 			break;
-		ret = nfs_wait_bit_killable(&q.key);
+		ret = nfs_wait_bit_killable(&q.key, TASK_KILLABLE);
 	} while (atomic_read(&c->io_count) != 0 && !ret);
 	finish_wait(wq, &q.wait);
 	return ret;
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -1466,11 +1466,11 @@ static bool pnfs_within_mdsthreshold(str
 }
 
 /* stop waiting if someone clears NFS_LAYOUT_RETRY_LAYOUTGET bit. */
-static int pnfs_layoutget_retry_bit_wait(struct wait_bit_key *key)
+static int pnfs_layoutget_retry_bit_wait(struct wait_bit_key *key, int mode)
 {
 	if (!test_bit(NFS_LAYOUT_RETRY_LAYOUTGET, key->flags))
 		return 1;
-	return nfs_wait_bit_killable(key);
+	return nfs_wait_bit_killable(key, mode);
 }
 
 static bool pnfs_prepare_to_retry_layoutget(struct pnfs_layout_hdr *lo)
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -145,7 +145,7 @@ __remove_wait_queue(wait_queue_head_t *h
 	list_del(&old->task_list);
 }
 
-typedef int wait_bit_action_f(struct wait_bit_key *);
+typedef int wait_bit_action_f(struct wait_bit_key *, int mode);
 void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr, void *key);
 void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key);
 void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode, int nr, void *key);
@@ -960,10 +960,10 @@ int wake_bit_function(wait_queue_t *wait
 	} while (0)
 
 
-extern int bit_wait(struct wait_bit_key *);
-extern int bit_wait_io(struct wait_bit_key *);
-extern int bit_wait_timeout(struct wait_bit_key *);
-extern int bit_wait_io_timeout(struct wait_bit_key *);
+extern int bit_wait(struct wait_bit_key *, int);
+extern int bit_wait_io(struct wait_bit_key *, int);
+extern int bit_wait_timeout(struct wait_bit_key *, int);
+extern int bit_wait_io_timeout(struct wait_bit_key *, int);
 
 /**
  * wait_on_bit - wait for a bit to be cleared
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -392,7 +392,7 @@ __wait_on_bit(wait_queue_head_t *wq, str
 	do {
 		prepare_to_wait(wq, &q->wait, mode);
 		if (test_bit(q->key.bit_nr, q->key.flags))
-			ret = (*action)(&q->key);
+			ret = (*action)(&q->key, mode);
 	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
 	finish_wait(wq, &q->wait);
 	return ret;
@@ -431,7 +431,7 @@ __wait_on_bit_lock(wait_queue_head_t *wq
 		prepare_to_wait_exclusive(wq, &q->wait, mode);
 		if (!test_bit(q->key.bit_nr, q->key.flags))
 			continue;
-		ret = action(&q->key);
+		ret = action(&q->key, mode);
 		if (!ret)
 			continue;
 		abort_exclusive_wait(wq, &q->wait, mode, &q->key);
@@ -581,43 +581,43 @@ void wake_up_atomic_t(atomic_t *p)
 }
 EXPORT_SYMBOL(wake_up_atomic_t);
 
-__sched int bit_wait(struct wait_bit_key *word)
+__sched int bit_wait(struct wait_bit_key *word, int mode)
 {
 	schedule();
-	if (signal_pending(current))
+	if (signal_pending_state(mode, current))
 		return -EINTR;
 	return 0;
 }
 EXPORT_SYMBOL(bit_wait);
 
-__sched int bit_wait_io(struct wait_bit_key *word)
+__sched int bit_wait_io(struct wait_bit_key *word, int mode)
 {
 	io_schedule();
-	if (signal_pending(current))
+	if (signal_pending_state(mode, current))
 		return -EINTR;
 	return 0;
 }
 EXPORT_SYMBOL(bit_wait_io);
 
-__sched int bit_wait_timeout(struct wait_bit_key *word)
+__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
 {
 	unsigned long now = READ_ONCE(jiffies);
 	if (time_after_eq(now, word->timeout))
 		return -EAGAIN;
 	schedule_timeout(word->timeout - now);
-	if (signal_pending(current))
+	if (signal_pending_state(mode, current))
 		return -EINTR;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(bit_wait_timeout);
 
-__sched int bit_wait_io_timeout(struct wait_bit_key *word)
+__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
 {
 	unsigned long now = READ_ONCE(jiffies);
 	if (time_after_eq(now, word->timeout))
 		return -EAGAIN;
 	io_schedule_timeout(word->timeout - now);
-	if (signal_pending(current))
+	if (signal_pending_state(mode, current))
 		return -EINTR;
 	return 0;
 }
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -250,11 +250,11 @@ void rpc_destroy_wait_queue(struct rpc_w
 }
 EXPORT_SYMBOL_GPL(rpc_destroy_wait_queue);
 
-static int rpc_wait_bit_killable(struct wait_bit_key *key)
+static int rpc_wait_bit_killable(struct wait_bit_key *key, int mode)
 {
-	if (fatal_signal_pending(current))
-		return -ERESTARTSYS;
 	freezable_schedule_unsafe();
+	if (signal_pending_state(mode, current))
+		return -ERESTARTSYS;
 	return 0;
 }
 

Re: [PATCH] sched/wait: Fix the signal handling fix

[Oleg Nesterov]

Peter, sorry. I didn't actually read this patch yet (and a lot of previous
emails). Will try tomorrow, I am not even sure I understand the problem(s)
correctly. But let me ask one question anyway,

On 12/13, Peter Zijlstra wrote:
>
> --- a/kernel/sched/wait.c
> +++ b/kernel/sched/wait.c
> @@ -392,7 +392,7 @@ __wait_on_bit(wait_queue_head_t *wq, str
>  	do {
>  		prepare_to_wait(wq, &q->wait, mode);
>  		if (test_bit(q->key.bit_nr, q->key.flags))
> -			ret = (*action)(&q->key);
> +			ret = (*action)(&q->key, mode);

And every action() should check signal_pending_state()...

So why we can't change __wait_on_bit/etc instead and remove all the signal-
pending checks from the callbacks? It seems that we can just check
signal_pending_state() before prepare_to_wait(). Or perhaps we can add
another helper which acts like prepare_to_wait_event().

Yes, some callers want -EINTR, some -ERESTARTSYS, but this shouldn't be a
problem.

And sorry if this was already discussed, another case when I am trying to
return to lkml with a lot of unread emails.

Oleg.

Re: [PATCH] sched/wait: Fix the signal handling fix

[Peter Zijlstra]

On Mon, Dec 14, 2015 at 07:50:04PM +0100, Oleg Nesterov wrote:
> > +			ret = (*action)(&q->key, mode);
> 
> And every action() should check signal_pending_state()...
> 
> So why we can't change __wait_on_bit/etc instead and remove all the signal-
> pending checks from the callbacks? It seems that we can just check
> signal_pending_state() before prepare_to_wait(). Or perhaps we can add
> another helper which acts like prepare_to_wait_event().
> 
> Yes, some callers want -EINTR, some -ERESTARTSYS, but this shouldn't be a
> problem.
> 
> And sorry if this was already discussed, another case when I am trying to
> return to lkml with a lot of unread emails.

Yes that looks like a viable cleanup. But at least now we have a base
that's working for everyone.

I'll try and do some patches tomorrow.