[PATCH AUTOSEL 4.14 47/95] fuse: fix possibly missed wake-up after abort

[PATCH AUTOSEL 4.14 47/95] fuse: fix possibly missed wake-up after abort

[Sasha Levin]

From: Miklos Szeredi <mszeredi@redhat.com>

[ Upstream commit 2d84a2d19b6150c6dbac1e6ebad9c82e4c123772 ]

In current fuse_drop_waiting() implementation it's possible that
fuse_wait_aborted() will not be woken up in the unlikely case that
fuse_abort_conn() + fuse_wait_aborted() runs in between checking
fc->connected and calling atomic_dec(&fc->num_waiting).

Do the atomic_dec_and_test() unconditionally, which also provides the
necessary barrier against reordering with the fc->connected check.

The explicit smp_mb() in fuse_wait_aborted() is not actually needed, since
the spin_unlock() in fuse_abort_conn() provides the necessary RELEASE
barrier after resetting fc->connected.  However, this is not a performance
sensitive path, and adding the explicit barrier makes it easier to
document.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: b8f95e5d13f5 ("fuse: umount should wait for all requests")
Cc: <stable@vger.kernel.org> #v4.19
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 fs/fuse/dev.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 63fd33383413..af78ceead2dc 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -133,9 +133,13 @@ static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
 
 static void fuse_drop_waiting(struct fuse_conn *fc)
 {
-	if (fc->connected) {
-		atomic_dec(&fc->num_waiting);
-	} else if (atomic_dec_and_test(&fc->num_waiting)) {
+	/*
+	 * lockess check of fc->connected is okay, because atomic_dec_and_test()
+	 * provides a memory barrier mached with the one in fuse_wait_aborted()
+	 * to ensure no wake-up is missed.
+	 */
+	if (atomic_dec_and_test(&fc->num_waiting) &&
+	    !READ_ONCE(fc->connected)) {
 		/* wake up aborters */
 		wake_up_all(&fc->blocked_waitq);
 	}
@@ -2170,6 +2174,8 @@ EXPORT_SYMBOL_GPL(fuse_abort_conn);
 
 void fuse_wait_aborted(struct fuse_conn *fc)
 {
+	/* matches implicit memory barrier in fuse_drop_waiting() */
+	smp_mb();
 	wait_event(fc->blocked_waitq, atomic_read(&fc->num_waiting) == 0);
 }
 
-- 
2.20.1

[PATCH AUTOSEL 4.14 50/95] fsnotify: generalize handling of extra event flags

[Sasha Levin]

From: Amir Goldstein <amir73il@gmail.com>

[ Upstream commit 007d1e8395eaa59b0e7ad9eb2b53a40859446a88 ]

FS_EVENT_ON_CHILD gets a special treatment in fsnotify() because it is
not a flag specifying an event type, but rather an extra flags that may
be reported along with another event and control the handling of the
event by the backend.

FS_ISDIR is also an "extra flag" and not an "event type" and therefore
desrves the same treatment. With inotify/dnotify backends it was never
possible to set FS_ISDIR in mark masks, so it did not matter.
With fanotify backend, mark adding code jumps through hoops to avoid
setting the FS_ISDIR in the commulative object mask.

Separate the constant ALL_FSNOTIFY_EVENTS to ALL_FSNOTIFY_FLAGS and
ALL_FSNOTIFY_EVENTS, so the latter can be used to test for specific
event types.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 fs/notify/fsnotify.c             | 7 +++----
 include/linux/fsnotify_backend.h | 9 +++++++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 506da82ff3f1..dc080c642dd0 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -192,7 +192,7 @@ static int send_to_group(struct inode *to_tell,
 			 struct fsnotify_iter_info *iter_info)
 {
 	struct fsnotify_group *group = NULL;
-	__u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
+	__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
 	__u32 marks_mask = 0;
 	__u32 marks_ignored_mask = 0;
 
@@ -256,8 +256,7 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
 	struct fsnotify_iter_info iter_info;
 	struct mount *mnt;
 	int ret = 0;
-	/* global tests shouldn't care about events on child only the specific event */
-	__u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
+	__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
 
 	if (data_is == FSNOTIFY_EVENT_PATH)
 		mnt = real_mount(((const struct path *)data)->mnt);
@@ -380,7 +379,7 @@ static __init int fsnotify_init(void)
 {
 	int ret;
 
-	BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
+	BUG_ON(hweight32(ALL_FSNOTIFY_BITS) != 23);
 
 	ret = init_srcu_struct(&fsnotify_mark_srcu);
 	if (ret)
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index ce74278a454a..81052313adeb 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -67,15 +67,20 @@
 
 #define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM)
 
+/* Events that can be reported to backends */
 #define ALL_FSNOTIFY_EVENTS (FS_ACCESS | FS_MODIFY | FS_ATTRIB | \
 			     FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN | \
 			     FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE | \
 			     FS_DELETE | FS_DELETE_SELF | FS_MOVE_SELF | \
 			     FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED | \
-			     FS_OPEN_PERM | FS_ACCESS_PERM | FS_EXCL_UNLINK | \
-			     FS_ISDIR | FS_IN_ONESHOT | FS_DN_RENAME | \
+			     FS_OPEN_PERM | FS_ACCESS_PERM | FS_DN_RENAME)
+
+/* Extra flags that may be reported with event or control handling of events */
+#define ALL_FSNOTIFY_FLAGS  (FS_EXCL_UNLINK | FS_ISDIR | FS_IN_ONESHOT | \
 			     FS_DN_MULTISHOT | FS_EVENT_ON_CHILD)
 
+#define ALL_FSNOTIFY_BITS   (ALL_FSNOTIFY_EVENTS | ALL_FSNOTIFY_FLAGS)
+
 struct fsnotify_group;
 struct fsnotify_event;
 struct fsnotify_mark;
-- 
2.20.1

Re: [PATCH AUTOSEL 4.14 50/95] fsnotify: generalize handling of extra event flags

[Jan Kara]

On Tue 07-05-19 01:37:39, Sasha Levin wrote:
> From: Amir Goldstein <amir73il@gmail.com>
> 
> [ Upstream commit 007d1e8395eaa59b0e7ad9eb2b53a40859446a88 ]
> 
> FS_EVENT_ON_CHILD gets a special treatment in fsnotify() because it is
> not a flag specifying an event type, but rather an extra flags that may
> be reported along with another event and control the handling of the
> event by the backend.
> 
> FS_ISDIR is also an "extra flag" and not an "event type" and therefore
> desrves the same treatment. With inotify/dnotify backends it was never
> possible to set FS_ISDIR in mark masks, so it did not matter.
> With fanotify backend, mark adding code jumps through hoops to avoid
> setting the FS_ISDIR in the commulative object mask.
> 
> Separate the constant ALL_FSNOTIFY_EVENTS to ALL_FSNOTIFY_FLAGS and
> ALL_FSNOTIFY_EVENTS, so the latter can be used to test for specific
> event types.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>

Sasha, why did you select this patch? It is just a cleanup with no user
visible effect and was done mostly to simplify implementing following
features...

								Honza

> ---
>  fs/notify/fsnotify.c             | 7 +++----
>  include/linux/fsnotify_backend.h | 9 +++++++--
>  2 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> index 506da82ff3f1..dc080c642dd0 100644
> --- a/fs/notify/fsnotify.c
> +++ b/fs/notify/fsnotify.c
> @@ -192,7 +192,7 @@ static int send_to_group(struct inode *to_tell,
>  			 struct fsnotify_iter_info *iter_info)
>  {
>  	struct fsnotify_group *group = NULL;
> -	__u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
> +	__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
>  	__u32 marks_mask = 0;
>  	__u32 marks_ignored_mask = 0;
>  
> @@ -256,8 +256,7 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>  	struct fsnotify_iter_info iter_info;
>  	struct mount *mnt;
>  	int ret = 0;
> -	/* global tests shouldn't care about events on child only the specific event */
> -	__u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
> +	__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
>  
>  	if (data_is == FSNOTIFY_EVENT_PATH)
>  		mnt = real_mount(((const struct path *)data)->mnt);
> @@ -380,7 +379,7 @@ static __init int fsnotify_init(void)
>  {
>  	int ret;
>  
> -	BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
> +	BUG_ON(hweight32(ALL_FSNOTIFY_BITS) != 23);
>  
>  	ret = init_srcu_struct(&fsnotify_mark_srcu);
>  	if (ret)
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index ce74278a454a..81052313adeb 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -67,15 +67,20 @@
>  
>  #define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM)
>  
> +/* Events that can be reported to backends */
>  #define ALL_FSNOTIFY_EVENTS (FS_ACCESS | FS_MODIFY | FS_ATTRIB | \
>  			     FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN | \
>  			     FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE | \
>  			     FS_DELETE | FS_DELETE_SELF | FS_MOVE_SELF | \
>  			     FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED | \
> -			     FS_OPEN_PERM | FS_ACCESS_PERM | FS_EXCL_UNLINK | \
> -			     FS_ISDIR | FS_IN_ONESHOT | FS_DN_RENAME | \
> +			     FS_OPEN_PERM | FS_ACCESS_PERM | FS_DN_RENAME)
> +
> +/* Extra flags that may be reported with event or control handling of events */
> +#define ALL_FSNOTIFY_FLAGS  (FS_EXCL_UNLINK | FS_ISDIR | FS_IN_ONESHOT | \
>  			     FS_DN_MULTISHOT | FS_EVENT_ON_CHILD)
>  
> +#define ALL_FSNOTIFY_BITS   (ALL_FSNOTIFY_EVENTS | ALL_FSNOTIFY_FLAGS)
> +
>  struct fsnotify_group;
>  struct fsnotify_event;
>  struct fsnotify_mark;
> -- 
> 2.20.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH AUTOSEL 4.14 50/95] fsnotify: generalize handling of extra event flags

[Sasha Levin]

On Tue, May 07, 2019 at 03:23:30PM +0200, Jan Kara wrote:
>On Tue 07-05-19 01:37:39, Sasha Levin wrote:
>> From: Amir Goldstein <amir73il@gmail.com>
>>
>> [ Upstream commit 007d1e8395eaa59b0e7ad9eb2b53a40859446a88 ]
>>
>> FS_EVENT_ON_CHILD gets a special treatment in fsnotify() because it is
>> not a flag specifying an event type, but rather an extra flags that may
>> be reported along with another event and control the handling of the
>> event by the backend.
>>
>> FS_ISDIR is also an "extra flag" and not an "event type" and therefore
>> desrves the same treatment. With inotify/dnotify backends it was never
>> possible to set FS_ISDIR in mark masks, so it did not matter.
>> With fanotify backend, mark adding code jumps through hoops to avoid
>> setting the FS_ISDIR in the commulative object mask.
>>
>> Separate the constant ALL_FSNOTIFY_EVENTS to ALL_FSNOTIFY_FLAGS and
>> ALL_FSNOTIFY_EVENTS, so the latter can be used to test for specific
>> event types.
>>
>> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>> Signed-off-by: Jan Kara <jack@suse.cz>
>> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
>
>Sasha, why did you select this patch? It is just a cleanup with no user
>visible effect and was done mostly to simplify implementing following
>features...

Sigh, my script picked up the patch after this one (by mistake). I've
dropped that one but missed this one twice(!). Thanks for the heads-up,
I'll drop it.

--
Thanks,
Sasha