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[ Upstream commit 387602d ]
Don't set WDM_READ flag in wdm_in_callback() for ZLP-s, otherwise when
userspace tries to poll for available data, it might - incorrectly -
believe there is something available, and when it tries to non-blocking
read it, it might get stuck in the read loop.
For example this is what glib does for non-blocking read (briefly):
1. poll()
2. if poll returns with non-zero, starts a read data loop:
a. loop on poll() (EINTR disabled)
b. if revents was set, reads data
I. if read returns with EINTR or EAGAIN, goto 2.a.
II. otherwise return with data
So if ZLP sets WDM_READ (#1), we expect data, and try to read it (#2).
But as that was a ZLP, and we are doing non-blocking read, wdm_read()
returns with EAGAIN (#2.b.I), so loop again, and try to read again
(#2.a.).
With glib, we might stuck in this loop forever, as EINTR is disabled
(#2.a).
Signed-off-by: Robert Hodaszi <[email protected]>
Acked-by: Oliver Neukum <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
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