usb: gadget: f_fs: Use stream_open() for endpoint files
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 9c225f26 ("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.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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