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FROMGIT: usb: gadget: f_fs: Use stream_open() for endpoint files

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Function fs endpoint file operations are synchronized via an interruptible
mutex wait. However we see threads that do ep file operations concurrently
are getting blocked for the mutex lock in __fdget_pos(). This is an
uninterruptible wait and we see hung task warnings and kernel panic
if hung_task_panic systcl is enabled if host does not send/receive
the data for long time.

The reason for threads getting blocked in __fdget_pos() is due to
the file position protection introduced by the commit 9c225f2655
("vfs: atomic f_pos accesses as per POSIX"). Since function fs
endpoint files does not have the notion of the file position, switch
to the stream mode. This will bypass the file position mutex and
threads will be blocked in interruptible state for the function fs
mutex.

It should not affects user space as we are only changing the task state
changes the task state from UNINTERRUPTIBLE to INTERRUPTIBLE while waiting
for the USB transfers to be finished. However there is a slight change to
the O_NONBLOCK behavior. Earlier threads that are using O_NONBLOCK are also
getting blocked inside fdget_pos(). Now they reach to function fs and error
code is returned. The non blocking behavior is actually honoured now.

Reviewed-by: John Keeping <john@metanate.com>
Signed-off-by: Pavankumar Kondeti <quic_pkondeti@quicinc.com>
Link: https://lore.kernel.org/r/1636712682-1226-1-git-send-email-quic_pkondeti@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit c76ef96fc0
 https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-next)
Bug: 206906138
Change-Id: Ifb99336a4da7587c7e71a6c45999a36948194d7a
Signed-off-by: Pavankumar Kondeti <quic_pkondeti@quicinc.com>
This commit is contained in:
Pavankumar Kondeti
2021-11-12 15:54:40 +05:30
committed by Greg Kroah-Hartman
parent d30938528e
commit 7a069c6071
1 changed files with 2 additions and 2 deletions
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4
drivers/usb/gadget/function/f_fs.c
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@@ -614,7 +614,7 @@ static int ffs_ep0_open(struct inode *inode, struct file *file)
file->private_data = ffs;
ffs_data_opened(ffs);
return 0;
return stream_open(inode, file);
}
static int ffs_ep0_release(struct inode *inode, struct file *file)
@@ -1152,7 +1152,7 @@ ffs_epfile_open(struct inode *inode, struct file *file)
file->private_data = epfile;
ffs_data_opened(epfile->ffs);
return 0;
return stream_open(inode, file);
}
static int ffs_aio_cancel(struct kiocb *kiocb)