xfs: fix COW writeback race

Due to the way how xfs_iomap_write_allocate tries to convert the whole
found extents from delalloc to real space we can run into a race
condition with multiple threads doing writes to this same extent.
For the non-COW case that is harmless as the only thing that can happen
is that we call xfs_bmapi_write on an extent that has already been
converted to a real allocation.  For COW writes where we move the extent
from the COW to the data fork after I/O completion the race is, however,
not quite as harmless.  In the worst case we are now calling
xfs_bmapi_write on a region that contains hole in the COW work, which
will trip up an assert in debug builds or lead to file system corruption
in non-debug builds.  This seems to be reproducible with workloads of
small O_DSYNC write, although so far I've not managed to come up with
a with an isolated reproducer.

The fix for the issue is relatively simple:  tell xfs_bmapi_write
that we are only asked to convert delayed allocations and skip holes
in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

path: root/include/acpi/button.h

#ifndef ACPI_BUTTON_H
#define ACPI_BUTTON_H

#include <linux/notifier.h>

#if IS_ENABLED(CONFIG_ACPI_BUTTON)
extern int acpi_lid_notifier_register(struct notifier_block *nb);
extern int acpi_lid_notifier_unregister(struct notifier_block *nb);
extern int acpi_lid_open(void);
#else
static inline int acpi_lid_notifier_register(struct notifier_block *nb)
{
	return 0;
}
static inline int acpi_lid_notifier_unregister(struct notifier_block *nb)
{
	return 0;
}
static inline int acpi_lid_open(void)
{
	return 1;
}
#endif /* IS_ENABLED(CONFIG_ACPI_BUTTON) */

#endif /* ACPI_BUTTON_H */