| Message ID | 20250318010318.3861682-1-ming.lei@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [V2] loop: move vfs_fsync() out of loop_update_dio() | expand |
On Tue, Mar 18, 2025 at 09:03:18AM +0800, Ming Lei wrote: > If vfs_flush() is called with queue frozen, the queue freeze lock may be > connected with FS internal lock, and lockdep warning can be triggered > because the queue freeze lock is connected with too many global or > sub-system locks. > > Fix the warning by moving vfs_fsync() out of loop_update_dio(): > > - vfs_fsync() is only needed when switching to dio > > - only loop_change_fd() and loop_configure() may switch from buffered > IO to direct IO, so call vfs_fsync() directly here. This way is safe > because either loop is in unbound, or new file isn't attached > > - for the other two cases of set_status and set_block_size, direct IO > can only become off, so no need to call vfs_fsync() > > Cc: Christoph Hellwig <hch@infradead.org> > Reported-by: Kun Hu <huk23@m.fudan.edu.cn> > Reported-by: Jiaji Qin <jjtan24@m.fudan.edu.cn> > Closes: https://lore.kernel.org/linux-block/359BC288-B0B1-4815-9F01-3A349B12E816@m.fudan.edu.cn/T/#u > Signed-off-by: Ming Lei <ming.lei@redhat.com> > --- > V2: > - update comment(Christoph) > > drivers/block/loop.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 8ca092303794..7ddb3cbc20fe 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -189,18 +189,12 @@ static bool lo_can_use_dio(struct loop_device *lo) > */ > static inline void loop_update_dio(struct loop_device *lo) > { > - bool dio_in_use = lo->lo_flags & LO_FLAGS_DIRECT_IO; > - > lockdep_assert_held(&lo->lo_mutex); > WARN_ON_ONCE(lo->lo_state == Lo_bound && > lo->lo_queue->mq_freeze_depth == 0); > > if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !lo_can_use_dio(lo)) > lo->lo_flags &= ~LO_FLAGS_DIRECT_IO; > - > - /* flush dirty pages before starting to issue direct I/O */ > - if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !dio_in_use) > - vfs_fsync(lo->lo_backing_file, 0); > } > > /** > @@ -637,6 +631,9 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, > if (get_loop_size(lo, file) != get_loop_size(lo, old_file)) > goto out_err; > > + /* may work in dio, so flush page cache before issuing dio */ > + vfs_fsync(file, 0); What does "may work" here mean? I think you mean something like: /* * We might switch to direct I/O mode for the loop device, write back * all dirty data the page cache now that so that the individual I/O * operations don't have to do that. */ ?
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 8ca092303794..7ddb3cbc20fe 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -189,18 +189,12 @@ static bool lo_can_use_dio(struct loop_device *lo) */ static inline void loop_update_dio(struct loop_device *lo) { - bool dio_in_use = lo->lo_flags & LO_FLAGS_DIRECT_IO; - lockdep_assert_held(&lo->lo_mutex); WARN_ON_ONCE(lo->lo_state == Lo_bound && lo->lo_queue->mq_freeze_depth == 0); if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !lo_can_use_dio(lo)) lo->lo_flags &= ~LO_FLAGS_DIRECT_IO; - - /* flush dirty pages before starting to issue direct I/O */ - if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !dio_in_use) - vfs_fsync(lo->lo_backing_file, 0); } /** @@ -637,6 +631,9 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, if (get_loop_size(lo, file) != get_loop_size(lo, old_file)) goto out_err; + /* may work in dio, so flush page cache before issuing dio */ + vfs_fsync(file, 0); + /* and ... switch */ disk_force_media_change(lo->lo_disk); memflags = blk_mq_freeze_queue(lo->lo_queue); @@ -1105,6 +1102,9 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode, if (error) goto out_unlock; + /* may work in dio, so flush page cache before issuing dio */ + vfs_fsync(file, 0); + loop_update_dio(lo); loop_sysfs_init(lo);
If vfs_flush() is called with queue frozen, the queue freeze lock may be connected with FS internal lock, and lockdep warning can be triggered because the queue freeze lock is connected with too many global or sub-system locks. Fix the warning by moving vfs_fsync() out of loop_update_dio(): - vfs_fsync() is only needed when switching to dio - only loop_change_fd() and loop_configure() may switch from buffered IO to direct IO, so call vfs_fsync() directly here. This way is safe because either loop is in unbound, or new file isn't attached - for the other two cases of set_status and set_block_size, direct IO can only become off, so no need to call vfs_fsync() Cc: Christoph Hellwig <hch@infradead.org> Reported-by: Kun Hu <huk23@m.fudan.edu.cn> Reported-by: Jiaji Qin <jjtan24@m.fudan.edu.cn> Closes: https://lore.kernel.org/linux-block/359BC288-B0B1-4815-9F01-3A349B12E816@m.fudan.edu.cn/T/#u Signed-off-by: Ming Lei <ming.lei@redhat.com> --- V2: - update comment(Christoph) drivers/block/loop.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)