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SubjectRe: [PATCH pm-for-3.2 1/2] freezer: reimplement wait_event_freezekillable using freezer_do_not_count/freezer_count()
Date
On Friday, November 04, 2011, Tejun Heo wrote:
> From: Oleg Nesterov <oleg@redhat.com>
>
> Commit 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake
> TASK_KILLABLE tasks too" updated fake_signal_wake_up() used by freezer
> to wake up KILLABLE tasks. Sending unsolicited wakeups to tasks in
> killable sleep is dangerous as there are code paths which depend on
> tasks not waking up spuriously from KILLABLE sleep.
>
> For example. sys_read() or page can sleep in TASK_KILLABLE assuming
> that wait/down/whatever _killable can only fail if we can not return
> to the usermode. TASK_TRACED is another obvious example.
>
> The offending commit was to resolve freezer hang during system PM
> operations caused by KILLABLE sleeps in network filesystems.
> wait_event_freezekillable(), which depends on the spurious KILLABLE
> wakeup, was added by f06ac72e92 "cifs, freezer: add
> wait_event_freezekillable and have cifs use it" to be used to
> implement killable & freezable sleeps in network filesystems.
>
> To prepare for reverting of 27920651fe, this patch reimplements
> wait_event_freezekillable() using freezer_do_not_count/freezer_count()
> so that it doesn't depend on the spurious KILLABLE wakeup. This isn't
> very nice but should do for now.
>
> tj: Refreshed patch to apply to linus/master and updated commit
> description on Rafael's request.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Jeff Layton <jlayton@redhat.com>
> LKML-Reference: <20111102175327.GA4446@redhat.com>

Applied to linux-pm/linux-next.

Thanks,
Rafael


> ---
> include/linux/freezer.h | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> Index: work/include/linux/freezer.h
> ===================================================================
> --- work.orig/include/linux/freezer.h
> +++ work/include/linux/freezer.h
> @@ -143,14 +143,9 @@ static inline void set_freezable_with_si
> #define wait_event_freezekillable(wq, condition) \
> ({ \
> int __retval; \
> - do { \
> - __retval = wait_event_killable(wq, \
> - (condition) || freezing(current)); \
> - if (__retval && !freezing(current)) \
> - break; \
> - else if (!(condition)) \
> - __retval = -ERESTARTSYS; \
> - } while (try_to_freeze()); \
> + freezer_do_not_count(); \
> + __retval = wait_event_killable(wq, (condition)); \
> + freezer_count(); \
> __retval; \
> })
>
>
>



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