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Subject[41/46] sysfs: Allow sysfs_notify_dirent to be called from interrupt context.
2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Neil Brown <neilb@suse.de>
commit 83db93f4de2d9ae441a491d1dc61c2204f0195de upstream.

sysfs_notify_dirent is a simple atomic operation that can be used to
alert user-space that new data can be read from a sysfs attribute.

Unfortunately it cannot currently be called from non-process context
because of its use of spin_lock which is sometimes taken with
interrupts enabled.

So change all lockers of sysfs_open_dirent_lock to disable interrupts,
thus making sysfs_notify_dirent safe to be called from non-process
context (as drivers/md does in md_safemode_timeout).

sysfs_get_open_dirent is (documented as being) only called from
process context, so it uses spin_lock_irq. Other places
use spin_lock_irqsave.

The usage for sysfs_notify_dirent in md_safemode_timeout was
introduced in 2.6.28, so this patch is suitable for that and more
recent kernels.

Reported-by: Joel Andres Granados <jgranado@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/sysfs/file.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -268,7 +268,7 @@ static int sysfs_get_open_dirent(struct
struct sysfs_open_dirent *od, *new_od = NULL;

retry:
- spin_lock(&sysfs_open_dirent_lock);
+ spin_lock_irq(&sysfs_open_dirent_lock);

if (!sd->s_attr.open && new_od) {
sd->s_attr.open = new_od;
@@ -281,7 +281,7 @@ static int sysfs_get_open_dirent(struct
list_add_tail(&buffer->list, &od->buffers);
}

- spin_unlock(&sysfs_open_dirent_lock);
+ spin_unlock_irq(&sysfs_open_dirent_lock);

if (od) {
kfree(new_od);
@@ -315,8 +315,9 @@ static void sysfs_put_open_dirent(struct
struct sysfs_buffer *buffer)
{
struct sysfs_open_dirent *od = sd->s_attr.open;
+ unsigned long flags;

- spin_lock(&sysfs_open_dirent_lock);
+ spin_lock_irqsave(&sysfs_open_dirent_lock, flags);

list_del(&buffer->list);
if (atomic_dec_and_test(&od->refcnt))
@@ -324,7 +325,7 @@ static void sysfs_put_open_dirent(struct
else
od = NULL;

- spin_unlock(&sysfs_open_dirent_lock);
+ spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);

kfree(od);
}
@@ -456,8 +457,9 @@ static unsigned int sysfs_poll(struct fi
void sysfs_notify_dirent(struct sysfs_dirent *sd)
{
struct sysfs_open_dirent *od;
+ unsigned long flags;

- spin_lock(&sysfs_open_dirent_lock);
+ spin_lock_irqsave(&sysfs_open_dirent_lock, flags);

od = sd->s_attr.open;
if (od) {
@@ -465,7 +467,7 @@ void sysfs_notify_dirent(struct sysfs_di
wake_up_interruptible(&od->poll);
}

- spin_unlock(&sysfs_open_dirent_lock);
+ spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
}
EXPORT_SYMBOL_GPL(sysfs_notify_dirent);




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