David Laight
2022-Jul-19 10:24 UTC
[Ocfs2-devel] [PATCH 2/3] ocfs2: Remove a useless spinlock
From: Christophe JAILLET> Sent: 19 July 2022 11:02 > > 'node_map_lock' is a spinlock only used to protect calls to set_bit(), > clear_bit() and test_bit(). > > {set|clear}_bit() are already atomic and don't need this extra spinlock. > test_bit() only reads the bitmap for a given bit. > > Remove this useless spinlock.It looks to me like the calling code is racy unless there is another lock in the callers. While map->map is protected, the result of test_bit() is stale - so can't be used for much. David> > Signed-off-by: Christophe JAILLET <christophe.jaillet at wanadoo.fr> > --- > test_bit() is NOT documented as an atomic function. However, I can't see > how it could return a wrong result here. > > So review with care. There is maybe something I don't think about that is > lurking here. > --- > fs/ocfs2/heartbeat.c | 11 ++++------- > fs/ocfs2/ocfs2.h | 2 -- > 2 files changed, 4 insertions(+), 9 deletions(-) > > diff --git a/fs/ocfs2/heartbeat.c b/fs/ocfs2/heartbeat.c > index 1d72e0788943..4863ad35c242 100644 > --- a/fs/ocfs2/heartbeat.c > +++ b/fs/ocfs2/heartbeat.c > @@ -35,7 +35,6 @@ static void ocfs2_node_map_init(struct ocfs2_node_map *map) > > void ocfs2_init_node_maps(struct ocfs2_super *osb) > { > - spin_lock_init(&osb->node_map_lock); > ocfs2_node_map_init(&osb->osb_recovering_orphan_dirs); > } > > @@ -67,9 +66,8 @@ void ocfs2_node_map_set_bit(struct ocfs2_super *osb, > if (bit==-1) > return; > BUG_ON(bit >= map->num_nodes); > - spin_lock(&osb->node_map_lock); > + > set_bit(bit, map->map); > - spin_unlock(&osb->node_map_lock); > } > > void ocfs2_node_map_clear_bit(struct ocfs2_super *osb, > @@ -79,9 +77,8 @@ void ocfs2_node_map_clear_bit(struct ocfs2_super *osb, > if (bit==-1) > return; > BUG_ON(bit >= map->num_nodes); > - spin_lock(&osb->node_map_lock); > + > clear_bit(bit, map->map); > - spin_unlock(&osb->node_map_lock); > } > > int ocfs2_node_map_test_bit(struct ocfs2_super *osb, > @@ -89,13 +86,13 @@ int ocfs2_node_map_test_bit(struct ocfs2_super *osb, > int bit) > { > int ret; > + > if (bit >= map->num_nodes) { > mlog(ML_ERROR, "bit=%d map->num_nodes=%d\n", bit, map->num_nodes); > BUG(); > } > - spin_lock(&osb->node_map_lock); > + > ret = test_bit(bit, map->map); > - spin_unlock(&osb->node_map_lock); > return ret; > } > > diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h > index 740b64238312..1df193b97c30 100644 > --- a/fs/ocfs2/ocfs2.h > +++ b/fs/ocfs2/ocfs2.h > @@ -302,8 +302,6 @@ struct ocfs2_super > > u32 *slot_recovery_generations; > > - spinlock_t node_map_lock; > - > u64 root_blkno; > u64 system_dir_blkno; > u64 bitmap_blkno; > -- > 2.34.1- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
Christophe JAILLET
2022-Jul-19 13:25 UTC
[Ocfs2-devel] [PATCH 2/3] ocfs2: Remove a useless spinlock
Le 19/07/2022 ? 12:24, David Laight a ?crit?:> From: Christophe JAILLET >> Sent: 19 July 2022 11:02 >> >> 'node_map_lock' is a spinlock only used to protect calls to set_bit(), >> clear_bit() and test_bit(). >> >> {set|clear}_bit() are already atomic and don't need this extra spinlock. >> test_bit() only reads the bitmap for a given bit. >> >> Remove this useless spinlock. > > It looks to me like the calling code is racy > unless there is another lock in the callers.The call chains are: ocfs2_recover_orphans() ocfs2_mark_recovering_orphan_dir() spin_lock(&osb->osb_lock); <-- osb_lock spinlock ocfs2_node_map_set_bit() <-- uses node_map_lock ... spin_unlock(&osb->osb_lock); ... ocfs2_clear_recovering_orphan_dir() ocfs2_node_map_clear_bit() <-- uses node_map_lock osb_lock is NOT taken ocfs2_check_orphan_recovery_state() spin_lock(&osb->osb_lock); <-- osb_lock spinlock ... ocfs2_node_map_test_bit() <-- uses node_map_lock ... spin_unlock(&osb->osb_lock); So the code looks already protected by the 'osb_lock' spinlock, but I don't know this code and ocfs2_mark_recovering_orphan_dir() looks tricky to me. (so some other eyes are much welcome)> While map->map is protected, the result of test_bit() > is stale - so can't be used for much. >Anyway, should there be a locking issue, it is there with or without my patch, right? CJ> David > >> >> Signed-off-by: Christophe JAILLET <christophe.jaillet at wanadoo.fr> >> --- >> test_bit() is NOT documented as an atomic function. However, I can't see >> how it could return a wrong result here. >> >> So review with care. There is maybe something I don't think about that is >> lurking here. >> --- >> fs/ocfs2/heartbeat.c | 11 ++++------- >> fs/ocfs2/ocfs2.h | 2 -- >> 2 files changed, 4 insertions(+), 9 deletions(-) >> >> diff --git a/fs/ocfs2/heartbeat.c b/fs/ocfs2/heartbeat.c >> index 1d72e0788943..4863ad35c242 100644 >> --- a/fs/ocfs2/heartbeat.c >> +++ b/fs/ocfs2/heartbeat.c >> @@ -35,7 +35,6 @@ static void ocfs2_node_map_init(struct ocfs2_node_map *map) >> >> void ocfs2_init_node_maps(struct ocfs2_super *osb) >> { >> - spin_lock_init(&osb->node_map_lock); >> ocfs2_node_map_init(&osb->osb_recovering_orphan_dirs); >> } >> >> @@ -67,9 +66,8 @@ void ocfs2_node_map_set_bit(struct ocfs2_super *osb, >> if (bit==-1) >> return; >> BUG_ON(bit >= map->num_nodes); >> - spin_lock(&osb->node_map_lock); >> + >> set_bit(bit, map->map); >> - spin_unlock(&osb->node_map_lock); >> } >> >> void ocfs2_node_map_clear_bit(struct ocfs2_super *osb, >> @@ -79,9 +77,8 @@ void ocfs2_node_map_clear_bit(struct ocfs2_super *osb, >> if (bit==-1) >> return; >> BUG_ON(bit >= map->num_nodes); >> - spin_lock(&osb->node_map_lock); >> + >> clear_bit(bit, map->map); >> - spin_unlock(&osb->node_map_lock); >> } >> >> int ocfs2_node_map_test_bit(struct ocfs2_super *osb, >> @@ -89,13 +86,13 @@ int ocfs2_node_map_test_bit(struct ocfs2_super *osb, >> int bit) >> { >> int ret; >> + >> if (bit >= map->num_nodes) { >> mlog(ML_ERROR, "bit=%d map->num_nodes=%d\n", bit, map->num_nodes); >> BUG(); >> } >> - spin_lock(&osb->node_map_lock); >> + >> ret = test_bit(bit, map->map); >> - spin_unlock(&osb->node_map_lock); >> return ret; >> } >> >> diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h >> index 740b64238312..1df193b97c30 100644 >> --- a/fs/ocfs2/ocfs2.h >> +++ b/fs/ocfs2/ocfs2.h >> @@ -302,8 +302,6 @@ struct ocfs2_super >> >> u32 *slot_recovery_generations; >> >> - spinlock_t node_map_lock; >> - >> u64 root_blkno; >> u64 system_dir_blkno; >> u64 bitmap_blkno; >> -- >> 2.34.1 > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) > >