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USB: update to Documentation
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this mentions a new deadlock due to advanced power management.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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Oliver Neukum authored and Greg Kroah-Hartman committed Aug 14, 2008
1 parent 230ffc7 commit f0fa746
Showing 1 changed file with 6 additions and 1 deletion.
7 changes: 6 additions & 1 deletion Documentation/usb/power-management.txt
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Expand Up @@ -436,7 +436,12 @@ post_reset; the USB core guarantees that this is true of internal
suspend/resume events as well.

If a driver wants to block all suspend/resume calls during some
critical section, it can simply acquire udev->pm_mutex.
critical section, it can simply acquire udev->pm_mutex. Note that
calls to resume may be triggered indirectly. Block IO due to memory
allocations can make the vm subsystem resume a device. Thus while
holding this lock you must not allocate memory with GFP_KERNEL or
GFP_NOFS.

Alternatively, if the critical section might call some of the
usb_autopm_* routines, the driver can avoid deadlock by doing:

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