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xfs: clean up filestreams helpers
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Move xfs_filestream_peek_ag, xxfs_filestream_get_ag and xfs_filestream_put_ag
from xfs_filestream.h to xfs_filestream.c where it's only callers are, and
remove the inline marker while we're at it to let the compiler decide on the
inlining.  Also don't return a value from xfs_filestream_put_ag because
we don't need it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
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Christoph Hellwig authored and Alex Elder committed Jul 26, 2010
1 parent 73523a2 commit 0664ce8
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Showing 2 changed files with 77 additions and 85 deletions.
80 changes: 77 additions & 3 deletions fs/xfs/xfs_filestream.c
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Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,82 @@ typedef struct fstrm_item
xfs_inode_t *pip; /* Parent directory inode pointer. */
} fstrm_item_t;

/*
* Allocation group filestream associations are tracked with per-ag atomic
* counters. These counters allow _xfs_filestream_pick_ag() to tell whether a
* particular AG already has active filestreams associated with it. The mount
* point's m_peraglock is used to protect these counters from per-ag array
* re-allocation during a growfs operation. When xfs_growfs_data_private() is
* about to reallocate the array, it calls xfs_filestream_flush() with the
* m_peraglock held in write mode.
*
* Since xfs_mru_cache_flush() guarantees that all the free functions for all
* the cache elements have finished executing before it returns, it's safe for
* the free functions to use the atomic counters without m_peraglock protection.
* This allows the implementation of xfs_fstrm_free_func() to be agnostic about
* whether it was called with the m_peraglock held in read mode, write mode or
* not held at all. The race condition this addresses is the following:
*
* - The work queue scheduler fires and pulls a filestream directory cache
* element off the LRU end of the cache for deletion, then gets pre-empted.
* - A growfs operation grabs the m_peraglock in write mode, flushes all the
* remaining items from the cache and reallocates the mount point's per-ag
* array, resetting all the counters to zero.
* - The work queue thread resumes and calls the free function for the element
* it started cleaning up earlier. In the process it decrements the
* filestreams counter for an AG that now has no references.
*
* With a shrinkfs feature, the above scenario could panic the system.
*
* All other uses of the following macros should be protected by either the
* m_peraglock held in read mode, or the cache's internal locking exposed by the
* interval between a call to xfs_mru_cache_lookup() and a call to
* xfs_mru_cache_done(). In addition, the m_peraglock must be held in read mode
* when new elements are added to the cache.
*
* Combined, these locking rules ensure that no associations will ever exist in
* the cache that reference per-ag array elements that have since been
* reallocated.
*/
static int
xfs_filestream_peek_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;

pag = xfs_perag_get(mp, agno);
ret = atomic_read(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}

static int
xfs_filestream_get_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;

pag = xfs_perag_get(mp, agno);
ret = atomic_inc_return(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}

static void
xfs_filestream_put_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;

pag = xfs_perag_get(mp, agno);
atomic_dec(&pag->pagf_fstrms);
xfs_perag_put(pag);
}

/*
* Scan the AGs starting at startag looking for an AG that isn't in use and has
Expand Down Expand Up @@ -351,16 +427,14 @@ xfs_fstrm_free_func(
{
fstrm_item_t *item = (fstrm_item_t *)data;
xfs_inode_t *ip = item->ip;
int ref;

ASSERT(ip->i_ino == ino);

xfs_iflags_clear(ip, XFS_IFILESTREAM);

/* Drop the reference taken on the AG when the item was added. */
ref = xfs_filestream_put_ag(ip->i_mount, item->ag);
xfs_filestream_put_ag(ip->i_mount, item->ag);

ASSERT(ref >= 0);
TRACE_FREE(ip->i_mount, ip, item->pip, item->ag,
xfs_filestream_peek_ag(ip->i_mount, item->ag));

Expand Down
82 changes: 0 additions & 82 deletions fs/xfs/xfs_filestream.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,88 +42,6 @@ extern ktrace_t *xfs_filestreams_trace_buf;

#endif

/*
* Allocation group filestream associations are tracked with per-ag atomic
* counters. These counters allow _xfs_filestream_pick_ag() to tell whether a
* particular AG already has active filestreams associated with it. The mount
* point's m_peraglock is used to protect these counters from per-ag array
* re-allocation during a growfs operation. When xfs_growfs_data_private() is
* about to reallocate the array, it calls xfs_filestream_flush() with the
* m_peraglock held in write mode.
*
* Since xfs_mru_cache_flush() guarantees that all the free functions for all
* the cache elements have finished executing before it returns, it's safe for
* the free functions to use the atomic counters without m_peraglock protection.
* This allows the implementation of xfs_fstrm_free_func() to be agnostic about
* whether it was called with the m_peraglock held in read mode, write mode or
* not held at all. The race condition this addresses is the following:
*
* - The work queue scheduler fires and pulls a filestream directory cache
* element off the LRU end of the cache for deletion, then gets pre-empted.
* - A growfs operation grabs the m_peraglock in write mode, flushes all the
* remaining items from the cache and reallocates the mount point's per-ag
* array, resetting all the counters to zero.
* - The work queue thread resumes and calls the free function for the element
* it started cleaning up earlier. In the process it decrements the
* filestreams counter for an AG that now has no references.
*
* With a shrinkfs feature, the above scenario could panic the system.
*
* All other uses of the following macros should be protected by either the
* m_peraglock held in read mode, or the cache's internal locking exposed by the
* interval between a call to xfs_mru_cache_lookup() and a call to
* xfs_mru_cache_done(). In addition, the m_peraglock must be held in read mode
* when new elements are added to the cache.
*
* Combined, these locking rules ensure that no associations will ever exist in
* the cache that reference per-ag array elements that have since been
* reallocated.
*/
/*
* xfs_filestream_peek_ag is only used in tracing code
*/
static inline int
xfs_filestream_peek_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;

pag = xfs_perag_get(mp, agno);
ret = atomic_read(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}

static inline int
xfs_filestream_get_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;

pag = xfs_perag_get(mp, agno);
ret = atomic_inc_return(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}

static inline int
xfs_filestream_put_ag(
xfs_mount_t *mp,
xfs_agnumber_t agno)
{
struct xfs_perag *pag;
int ret;

pag = xfs_perag_get(mp, agno);
ret = atomic_dec_return(&pag->pagf_fstrms);
xfs_perag_put(pag);
return ret;
}

/* allocation selection flags */
typedef enum xfs_fstrm_alloc {
XFS_PICK_USERDATA = 1,
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