Re: [PATCH v2] btrfs: don't take dev_replace rwsem on task already

[Johannes Thumshirn]

This is to fold in if we decide to go by pid instead of a task_struct.

---
 fs/btrfs/dev-replace.c | 4 ++--
 fs/btrfs/fs.h          | 3 ++-
 fs/btrfs/volumes.c     | 8 +++++---
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 604399e59a3d..a1efb8de8170 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -641,7 +641,7 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 		return ret;
 
 	down_write(&dev_replace->rwsem);
-	dev_replace->replace_task = current;
+	dev_replace->replace_task = current->pid;
 	switch (dev_replace->replace_state) {
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
@@ -995,7 +995,7 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
 	list_add(&tgt_device->dev_alloc_list, &fs_devices->alloc_list);
 	fs_devices->rw_devices++;
 
-	dev_replace->replace_task = NULL;
+	dev_replace->replace_task = 0;
 	up_write(&dev_replace->rwsem);
 	btrfs_rm_dev_replace_blocked(fs_info);
 
diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index cbfb225858a5..a30978f29a59 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -3,6 +3,7 @@
 #ifndef BTRFS_FS_H
 #define BTRFS_FS_H
 
+#include "linux/types.h"
 #include <linux/blkdev.h>
 #include <linux/sizes.h>
 #include <linux/time64.h>
@@ -318,7 +319,7 @@ struct btrfs_dev_replace {
 	struct percpu_counter bio_counter;
 	wait_queue_head_t replace_wait;
 
-	struct task_struct *replace_task;
+	pid_t replace_task;
 };
 
 /*
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 995b0647f538..c3f53a59cbf3 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6480,7 +6480,7 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
 	max_len = btrfs_max_io_len(map, map_offset, &io_geom);
 	*length = min_t(u64, map->chunk_len - map_offset, max_len);
 
-	if (dev_replace->replace_task != current)
+	if (dev_replace->replace_task != current->pid)
 		down_read(&dev_replace->rwsem);
 
 	dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);
@@ -6488,7 +6488,8 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
 	 * Hold the semaphore for read during the whole operation, write is
 	 * requested at commit time but must wait.
 	 */
-	if (!dev_replace_is_ongoing && dev_replace->replace_task != current)
+	if (!dev_replace_is_ongoing &&
+	    dev_replace->replace_task != current->pid)
 		up_read(&dev_replace->rwsem);
 
 	switch (map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
@@ -6628,7 +6629,8 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
 	bioc->mirror_num = io_geom.mirror_num;
 
 out:
-	if (dev_replace_is_ongoing && dev_replace->replace_task != current) {
+	if (dev_replace_is_ongoing &&
+	    dev_replace->replace_task != current->pid) {
 		lockdep_assert_held(&dev_replace->rwsem);
 		/* Unlock and let waiting writers proceed */
 		up_read(&dev_replace->rwsem);
-- 
2.43.0