| Message ID | 20160926160806.GB6748@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon 26-09-16 18:08:06, Oleg Nesterov wrote: > sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the > false-positives. Now that xfs was fixed by Dave's commit dbad7c993053 > ("xfs: stop holding ILOCK over filldir callbacks") we can remove it and > change freeze_super() and thaw_super() to run with s_writers.rw_sem > locks held; we add two trivial helpers for that, sb_freeze_release() > and sb_freeze_acquire(). > > xfstests-dev/check `grep -il freeze tests/*/???` does not trigger any > warning from lockdep. ... > +/* > + * We are going to return to userspace and forget about these locks, the > + * ownership goes to the caller of thaw_super() which does unlock(). > + */ > +static void sb_freeze_release(struct super_block *sb) > +{ > + int level; > + > + for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) > + percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_); > +} > + > +/* > + * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb). > + */ > +static void sb_freeze_acquire(struct super_block *sb) Can we call this lockdep_sb_freeze_acquire() or something like that so that it is clear this is only about lockdep annotations? Similarly with sb_freeze_unlock()... Other than that the change looks good to me (and I hope you really tested there are no more lockdep false positives ;). Honza > { > int level; > > for (level = 0; level < SB_FREEZE_LEVELS; ++level) > percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_); > +} > + > +static void sb_freeze_unlock(struct super_block *sb) > +{ > + int level; > > for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) > percpu_up_write(sb->s_writers.rw_sem + level); > @@ -1328,6 +1337,7 @@ int freeze_super(struct super_block *sb) > * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super(). > */ > sb->s_writers.frozen = SB_FREEZE_COMPLETE; > + sb_freeze_release(sb); > up_write(&sb->s_umount); > return 0; > } > @@ -1354,11 +1364,14 @@ int thaw_super(struct super_block *sb) > goto out; > } > > + sb_freeze_acquire(sb); > + > if (sb->s_op->unfreeze_fs) { > error = sb->s_op->unfreeze_fs(sb); > if (error) { > printk(KERN_ERR > "VFS:Filesystem thaw failed\n"); > + sb_freeze_release(sb); > up_write(&sb->s_umount); > return error; > } > -- > 2.5.0 > >
diff --git a/fs/super.c b/fs/super.c index 2549896c..a9757e1 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1214,25 +1214,34 @@ EXPORT_SYMBOL(__sb_start_write); static void sb_wait_write(struct super_block *sb, int level) { percpu_down_write(sb->s_writers.rw_sem + level-1); - /* - * We are going to return to userspace and forget about this lock, the - * ownership goes to the caller of thaw_super() which does unlock. - * - * FIXME: we should do this before return from freeze_super() after we - * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super() - * should re-acquire these locks before s_op->unfreeze_fs(sb). However - * this leads to lockdep false-positives, so currently we do the early - * release right after acquire. - */ - percpu_rwsem_release(sb->s_writers.rw_sem + level-1, 0, _THIS_IP_); } -static void sb_freeze_unlock(struct super_block *sb) +/* + * We are going to return to userspace and forget about these locks, the + * ownership goes to the caller of thaw_super() which does unlock(). + */ +static void sb_freeze_release(struct super_block *sb) +{ + int level; + + for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) + percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_); +} + +/* + * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb). + */ +static void sb_freeze_acquire(struct super_block *sb) { int level; for (level = 0; level < SB_FREEZE_LEVELS; ++level) percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_); +} + +static void sb_freeze_unlock(struct super_block *sb) +{ + int level; for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) percpu_up_write(sb->s_writers.rw_sem + level); @@ -1328,6 +1337,7 @@ int freeze_super(struct super_block *sb) * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super(). */ sb->s_writers.frozen = SB_FREEZE_COMPLETE; + sb_freeze_release(sb); up_write(&sb->s_umount); return 0; } @@ -1354,11 +1364,14 @@ int thaw_super(struct super_block *sb) goto out; } + sb_freeze_acquire(sb); + if (sb->s_op->unfreeze_fs) { error = sb->s_op->unfreeze_fs(sb); if (error) { printk(KERN_ERR "VFS:Filesystem thaw failed\n"); + sb_freeze_release(sb); up_write(&sb->s_umount); return error; }
sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the false-positives. Now that xfs was fixed by Dave's commit dbad7c993053 ("xfs: stop holding ILOCK over filldir callbacks") we can remove it and change freeze_super() and thaw_super() to run with s_writers.rw_sem locks held; we add two trivial helpers for that, sb_freeze_release() and sb_freeze_acquire(). xfstests-dev/check `grep -il freeze tests/*/???` does not trigger any warning from lockdep. Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- fs/super.c | 37 +++++++++++++++++++++++++------------ 1 file changed, 25 insertions(+), 12 deletions(-)