Re: [PATCH v3 04/49] mm: shrinker: remove redundant shrinker_rwsem in debugfs operations
From: Simon Horman <hidden>
Date: 2023-07-28 08:14:00
Also in:
dm-devel, dri-devel, kvm, linux-arm-msm, linux-bcache, linux-btrfs, linux-ext4, linux-f2fs-devel, linux-fsdevel, linux-mm, linux-nfs, linux-raid, linux-xfs, lkml, rcu, xen-devel
On Thu, Jul 27, 2023 at 04:04:17PM +0800, Qi Zheng wrote:
quoted hunk ↗ jump to hunk
The debugfs_remove_recursive() will wait for debugfs_file_put() to return, so the shrinker will not be freed when doing debugfs operations (such as shrinker_debugfs_count_show() and shrinker_debugfs_scan_write()), so there is no need to hold shrinker_rwsem during debugfs operations. Signed-off-by: Qi Zheng <redacted> Reviewed-by: Muchun Song <redacted> --- mm/shrinker_debug.c | 14 -------------- 1 file changed, 14 deletions(-)diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c index 3ab53fad8876..f1becfd45853 100644 --- a/mm/shrinker_debug.c +++ b/mm/shrinker_debug.c@@ -55,11 +55,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v) if (!count_per_node) return -ENOMEM; - ret = down_read_killable(&shrinker_rwsem); - if (ret) { - kfree(count_per_node); - return ret; - } rcu_read_lock();
Hi Qi Zheng,
As can be seen in the next hunk, this function returns 'ret'.
However, with this change 'ret' is uninitialised unless
signal_pending() returns non-zero in the while loop below.
This is flagged in a clan-16 W=1 build.
mm/shrinker_debug.c:87:11: warning: variable 'ret' is used uninitialized whenever 'do' loop exits because its condition is false [-Wsometimes-uninitialized]
} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/shrinker_debug.c:92:9: note: uninitialized use occurs here
return ret;
^~~
mm/shrinker_debug.c:87:11: note: remove the condition if it is always true
} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1
mm/shrinker_debug.c:77:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
if (!memcg_aware) {
^~~~~~~~~~~~
mm/shrinker_debug.c:92:9: note: uninitialized use occurs here
return ret;
^~~
mm/shrinker_debug.c:77:3: note: remove the 'if' if its condition is always false
if (!memcg_aware) {
^~~~~~~~~~~~~~~~~~~
mm/shrinker_debug.c:52:9: note: initialize the variable 'ret' to silence this warning
int ret, nid;
^
= 0
quoted hunk ↗ jump to hunk
memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;@@ -92,7 +87,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v) } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); rcu_read_unlock(); - up_read(&shrinker_rwsem); kfree(count_per_node); return ret;
...