The hugetlb cgroup usage wait loops in charge_reserved_hugetlb.sh were
unbounded and could hang forever if the expected cgroup file value never
appears (e.g. due to write_to_hugetlbfs in Error mapping).

--- Error log ---
  # uname -r
  6.12.0-xxx.el10.aarch64+64k

  # ls /sys/kernel/mm/hugepages/hugepages-*
  hugepages-16777216kB/  hugepages-2048kB/  hugepages-524288kB/

  #./charge_reserved_hugetlb.sh -cgroup-v2
  # -----------------------------------------
  ...
  # nr hugepages = 10
  # writing cgroup limit: 5368709120
  # writing reseravation limit: 5368709120
  ...
  # write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  ...

Introduce a small helper, wait_for_file_value(), and use it for:
  - waiting for reservation usage to drop to 0,
  - waiting for reservation usage to reach a given size,
  - waiting for fault usage to reach a given size.

This makes the waits consistent and adds a hard timeout (60 tries with
1s sleep) so the test fails instead of stalling indefinitely.

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Waiman Long <longman@redhat.com>
---
 .../selftests/mm/charge_reserved_hugetlb.sh   | 51 +++++++++++--------
 1 file changed, 30 insertions(+), 21 deletions(-)

diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
index fa6713892d82..447769657634 100755
--- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
+++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
@@ -100,7 +100,7 @@ function setup_cgroup() {
   echo writing cgroup limit: "$cgroup_limit"
   echo "$cgroup_limit" >$cgroup_path/$name/hugetlb.${MB}MB.$fault_limit_file
 
-  echo writing reseravation limit: "$reservation_limit"
+  echo writing reservation limit: "$reservation_limit"
   echo "$reservation_limit" > \
     $cgroup_path/$name/hugetlb.${MB}MB.$reservation_limit_file
 
@@ -112,41 +112,50 @@ function setup_cgroup() {
   fi
 }
 
+function wait_for_file_value() {
+  local path="$1"
+  local expect="$2"
+  local max_tries=60
+
+  if [[ ! -r "$path" ]]; then
+    echo "ERROR: cannot read '$path', missing or permission denied"
+    return 1
+  fi
+
+  for ((i=1; i<=max_tries; i++)); do
+    local cur="$(cat "$path")"
+    if [[ "$cur" == "$expect" ]]; then
+      return 0
+    fi
+    echo "Waiting for $path to become '$expect' (current: '$cur') (try $i/$max_tries)"
+    sleep 1
+  done
+
+  echo "ERROR: timeout waiting for $path to become '$expect'"
+  return 1
+}
+
 function wait_for_hugetlb_memory_to_get_depleted() {
   local cgroup="$1"
   local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
-  # Wait for hugetlbfs memory to get depleted.
-  while [ $(cat $path) != 0 ]; do
-    echo Waiting for hugetlb memory to get depleted.
-    cat $path
-    sleep 0.5
-  done
+
+  wait_for_file_value "$path" "0"
 }
 
 function wait_for_hugetlb_memory_to_get_reserved() {
   local cgroup="$1"
   local size="$2"
-
   local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
-  # Wait for hugetlbfs memory to get written.
-  while [ $(cat $path) != $size ]; do
-    echo Waiting for hugetlb memory reservation to reach size $size.
-    cat $path
-    sleep 0.5
-  done
+
+  wait_for_file_value "$path" "$size"
 }
 
 function wait_for_hugetlb_memory_to_get_written() {
   local cgroup="$1"
   local size="$2"
-
   local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$fault_usage_file"
-  # Wait for hugetlbfs memory to get written.
-  while [ $(cat $path) != $size ]; do
-    echo Waiting for hugetlb memory to reach size $size.
-    cat $path
-    sleep 0.5
-  done
+
+  wait_for_file_value "$path" "$size"
 }
 
 function write_hugetlbfs_and_get_usage() {
-- 
2.49.0

On 12/21/25 13:26, Li Wang wrote:
> The hugetlb cgroup usage wait loops in charge_reserved_hugetlb.sh were
> unbounded and could hang forever if the expected cgroup file value never
> appears (e.g. due to write_to_hugetlbfs in Error mapping).
> 
> --- Error log ---
>    # uname -r
>    6.12.0-xxx.el10.aarch64+64k
> 
>    # ls /sys/kernel/mm/hugepages/hugepages-*
>    hugepages-16777216kB/  hugepages-2048kB/  hugepages-524288kB/
> 
>    #./charge_reserved_hugetlb.sh -cgroup-v2
>    # -----------------------------------------
>    ...
>    # nr hugepages = 10
>    # writing cgroup limit: 5368709120
>    # writing reseravation limit: 5368709120
>    ...
>    # write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    ...
> 
> Introduce a small helper, wait_for_file_value(), and use it for:
>    - waiting for reservation usage to drop to 0,
>    - waiting for reservation usage to reach a given size,
>    - waiting for fault usage to reach a given size.
> 
> This makes the waits consistent and adds a hard timeout (60 tries with
> 1s sleep) so the test fails instead of stalling indefinitely.
> 
> Signed-off-by: Li Wang <liwang@redhat.com>
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> ---
>   .../selftests/mm/charge_reserved_hugetlb.sh   | 51 +++++++++++--------
>   1 file changed, 30 insertions(+), 21 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> index fa6713892d82..447769657634 100755
> --- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> +++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> @@ -100,7 +100,7 @@ function setup_cgroup() {
>     echo writing cgroup limit: "$cgroup_limit"
>     echo "$cgroup_limit" >$cgroup_path/$name/hugetlb.${MB}MB.$fault_limit_file
>   
> -  echo writing reseravation limit: "$reservation_limit"
> +  echo writing reservation limit: "$reservation_limit"
>     echo "$reservation_limit" > \
>       $cgroup_path/$name/hugetlb.${MB}MB.$reservation_limit_file
>   
> @@ -112,41 +112,50 @@ function setup_cgroup() {
>     fi
>   }
>   
> +function wait_for_file_value() {
> +  local path="$1"
> +  local expect="$2"
> +  local max_tries=60
> +
> +  if [[ ! -r "$path" ]]; then
> +    echo "ERROR: cannot read '$path', missing or permission denied"
> +    return 1
> +  fi
> +
> +  for ((i=1; i<=max_tries; i++)); do
> +    local cur="$(cat "$path")"
> +    if [[ "$cur" == "$expect" ]]; then
> +      return 0
> +    fi
> +    echo "Waiting for $path to become '$expect' (current: '$cur') (try $i/$max_tries)"
> +    sleep 1
> +  done
> +
> +  echo "ERROR: timeout waiting for $path to become '$expect'"
> +  return 1
> +}
> +
>   function wait_for_hugetlb_memory_to_get_depleted() {
>     local cgroup="$1"
>     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
> -  # Wait for hugetlbfs memory to get depleted.
> -  while [ $(cat $path) != 0 ]; do
> -    echo Waiting for hugetlb memory to get depleted.
> -    cat $path
> -    sleep 0.5
> -  done
> +
> +  wait_for_file_value "$path" "0"
>   }
>   
>   function wait_for_hugetlb_memory_to_get_reserved() {
>     local cgroup="$1"
>     local size="$2"
> -
>     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
> -  # Wait for hugetlbfs memory to get written.
> -  while [ $(cat $path) != $size ]; do
> -    echo Waiting for hugetlb memory reservation to reach size $size.
> -    cat $path
> -    sleep 0.5
> -  done
> +
> +  wait_for_file_value "$path" "$size"
>   }
>   
>   function wait_for_hugetlb_memory_to_get_written() {
>     local cgroup="$1"
>     local size="$2"
> -
>     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$fault_usage_file"
> -  # Wait for hugetlbfs memory to get written.
> -  while [ $(cat $path) != $size ]; do
> -    echo Waiting for hugetlb memory to reach size $size.
> -    cat $path
> -    sleep 0.5
> -  done
> +
> +  wait_for_file_value "$path" "$size"
>   }
>   
>   function write_hugetlbfs_and_get_usage() {

It would indeed be cleaner to propagate the error and make it clearer 
how we then cleanly abort the test.

But if it keeps working for the time beiing, fine with me

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

-- 
Cheers

David

On 12/21/25 7:26 AM, Li Wang wrote:
> The hugetlb cgroup usage wait loops in charge_reserved_hugetlb.sh were
> unbounded and could hang forever if the expected cgroup file value never
> appears (e.g. due to write_to_hugetlbfs in Error mapping).
>
> --- Error log ---
>    # uname -r
>    6.12.0-xxx.el10.aarch64+64k
>
>    # ls /sys/kernel/mm/hugepages/hugepages-*
>    hugepages-16777216kB/  hugepages-2048kB/  hugepages-524288kB/
>
>    #./charge_reserved_hugetlb.sh -cgroup-v2
>    # -----------------------------------------
>    ...
>    # nr hugepages = 10
>    # writing cgroup limit: 5368709120
>    # writing reseravation limit: 5368709120
>    ...
>    # write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    # Waiting for hugetlb memory reservation to reach size 2684354560.
>    # 0
>    ...
>
> Introduce a small helper, wait_for_file_value(), and use it for:
>    - waiting for reservation usage to drop to 0,
>    - waiting for reservation usage to reach a given size,
>    - waiting for fault usage to reach a given size.
>
> This makes the waits consistent and adds a hard timeout (60 tries with
> 1s sleep) so the test fails instead of stalling indefinitely.
>
> Signed-off-by: Li Wang <liwang@redhat.com>
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> ---
>   .../selftests/mm/charge_reserved_hugetlb.sh   | 51 +++++++++++--------
>   1 file changed, 30 insertions(+), 21 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> index fa6713892d82..447769657634 100755
> --- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> +++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> @@ -100,7 +100,7 @@ function setup_cgroup() {
>     echo writing cgroup limit: "$cgroup_limit"
>     echo "$cgroup_limit" >$cgroup_path/$name/hugetlb.${MB}MB.$fault_limit_file
>   
> -  echo writing reseravation limit: "$reservation_limit"
> +  echo writing reservation limit: "$reservation_limit"
>     echo "$reservation_limit" > \
>       $cgroup_path/$name/hugetlb.${MB}MB.$reservation_limit_file
>   
> @@ -112,41 +112,50 @@ function setup_cgroup() {
>     fi
>   }
>   
> +function wait_for_file_value() {
> +  local path="$1"
> +  local expect="$2"
> +  local max_tries=60
> +
> +  if [[ ! -r "$path" ]]; then
> +    echo "ERROR: cannot read '$path', missing or permission denied"
> +    return 1
> +  fi
> +
> +  for ((i=1; i<=max_tries; i++)); do
> +    local cur="$(cat "$path")"
> +    if [[ "$cur" == "$expect" ]]; then
> +      return 0
> +    fi
> +    echo "Waiting for $path to become '$expect' (current: '$cur') (try $i/$max_tries)"
> +    sleep 1
> +  done
> +
> +  echo "ERROR: timeout waiting for $path to become '$expect'"
> +  return 1
> +}
> +
>   function wait_for_hugetlb_memory_to_get_depleted() {
>     local cgroup="$1"
>     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
> -  # Wait for hugetlbfs memory to get depleted.
> -  while [ $(cat $path) != 0 ]; do
> -    echo Waiting for hugetlb memory to get depleted.
> -    cat $path
> -    sleep 0.5
> -  done
> +
> +  wait_for_file_value "$path" "0"
>   }
>   
>   function wait_for_hugetlb_memory_to_get_reserved() {
>     local cgroup="$1"
>     local size="$2"
> -
>     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
> -  # Wait for hugetlbfs memory to get written.
> -  while [ $(cat $path) != $size ]; do
> -    echo Waiting for hugetlb memory reservation to reach size $size.
> -    cat $path
> -    sleep 0.5
> -  done
> +
> +  wait_for_file_value "$path" "$size"
>   }
>   
>   function wait_for_hugetlb_memory_to_get_written() {
>     local cgroup="$1"
>     local size="$2"
> -
>     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$fault_usage_file"
> -  # Wait for hugetlbfs memory to get written.
> -  while [ $(cat $path) != $size ]; do
> -    echo Waiting for hugetlb memory to reach size $size.
> -    cat $path
> -    sleep 0.5
> -  done
> +
> +  wait_for_file_value "$path" "$size"
>   }
>   
>   function write_hugetlbfs_and_get_usage() {

wait_for_file_value() now return 0 onr success and 1 on timeout. 
However, none of the callers of the wait_for_hugetlb_memory* are 
checking their return values and acting accordingly. Are we expecting 
that the test will show failure because the waiting isn't completed or 
should we explicitly exit with ksft_fail (1) value?

Cheers,
Longman

On Mon, Dec 22, 2025 at 4:30 AM Waiman Long <llong@redhat.com> wrote:
>
>
> On 12/21/25 7:26 AM, Li Wang wrote:
> > The hugetlb cgroup usage wait loops in charge_reserved_hugetlb.sh were
> > unbounded and could hang forever if the expected cgroup file value never
> > appears (e.g. due to write_to_hugetlbfs in Error mapping).
> >
> > --- Error log ---
> >    # uname -r
> >    6.12.0-xxx.el10.aarch64+64k
> >
> >    # ls /sys/kernel/mm/hugepages/hugepages-*
> >    hugepages-16777216kB/  hugepages-2048kB/  hugepages-524288kB/
> >
> >    #./charge_reserved_hugetlb.sh -cgroup-v2
> >    # -----------------------------------------
> >    ...
> >    # nr hugepages = 10
> >    # writing cgroup limit: 5368709120
> >    # writing reseravation limit: 5368709120
> >    ...
> >    # write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
> >    # Waiting for hugetlb memory reservation to reach size 2684354560.
> >    # 0
> >    # Waiting for hugetlb memory reservation to reach size 2684354560.
> >    # 0
> >    # Waiting for hugetlb memory reservation to reach size 2684354560.
> >    # 0
> >    # Waiting for hugetlb memory reservation to reach size 2684354560.
> >    # 0
> >    # Waiting for hugetlb memory reservation to reach size 2684354560.
> >    # 0
> >    # Waiting for hugetlb memory reservation to reach size 2684354560.
> >    # 0
> >    ...
> >
> > Introduce a small helper, wait_for_file_value(), and use it for:
> >    - waiting for reservation usage to drop to 0,
> >    - waiting for reservation usage to reach a given size,
> >    - waiting for fault usage to reach a given size.
> >
> > This makes the waits consistent and adds a hard timeout (60 tries with
> > 1s sleep) so the test fails instead of stalling indefinitely.
> >
> > Signed-off-by: Li Wang <liwang@redhat.com>
> > Cc: David Hildenbrand <david@kernel.org>
> > Cc: Mark Brown <broonie@kernel.org>
> > Cc: Shuah Khan <shuah@kernel.org>
> > Cc: Waiman Long <longman@redhat.com>
> > ---
> >   .../selftests/mm/charge_reserved_hugetlb.sh   | 51 +++++++++++--------
> >   1 file changed, 30 insertions(+), 21 deletions(-)
> >
> > diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> > index fa6713892d82..447769657634 100755
> > --- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> > +++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> > @@ -100,7 +100,7 @@ function setup_cgroup() {
> >     echo writing cgroup limit: "$cgroup_limit"
> >     echo "$cgroup_limit" >$cgroup_path/$name/hugetlb.${MB}MB.$fault_limit_file
> >
> > -  echo writing reseravation limit: "$reservation_limit"
> > +  echo writing reservation limit: "$reservation_limit"
> >     echo "$reservation_limit" > \
> >       $cgroup_path/$name/hugetlb.${MB}MB.$reservation_limit_file
> >
> > @@ -112,41 +112,50 @@ function setup_cgroup() {
> >     fi
> >   }
> >
> > +function wait_for_file_value() {
> > +  local path="$1"
> > +  local expect="$2"
> > +  local max_tries=60
> > +
> > +  if [[ ! -r "$path" ]]; then
> > +    echo "ERROR: cannot read '$path', missing or permission denied"
> > +    return 1
> > +  fi
> > +
> > +  for ((i=1; i<=max_tries; i++)); do
> > +    local cur="$(cat "$path")"
> > +    if [[ "$cur" == "$expect" ]]; then
> > +      return 0
> > +    fi
> > +    echo "Waiting for $path to become '$expect' (current: '$cur') (try $i/$max_tries)"
> > +    sleep 1
> > +  done
> > +
> > +  echo "ERROR: timeout waiting for $path to become '$expect'"
> > +  return 1
> > +}
> > +
> >   function wait_for_hugetlb_memory_to_get_depleted() {
> >     local cgroup="$1"
> >     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
> > -  # Wait for hugetlbfs memory to get depleted.
> > -  while [ $(cat $path) != 0 ]; do
> > -    echo Waiting for hugetlb memory to get depleted.
> > -    cat $path
> > -    sleep 0.5
> > -  done
> > +
> > +  wait_for_file_value "$path" "0"
> >   }
> >
> >   function wait_for_hugetlb_memory_to_get_reserved() {
> >     local cgroup="$1"
> >     local size="$2"
> > -
> >     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
> > -  # Wait for hugetlbfs memory to get written.
> > -  while [ $(cat $path) != $size ]; do
> > -    echo Waiting for hugetlb memory reservation to reach size $size.
> > -    cat $path
> > -    sleep 0.5
> > -  done
> > +
> > +  wait_for_file_value "$path" "$size"
> >   }
> >
> >   function wait_for_hugetlb_memory_to_get_written() {
> >     local cgroup="$1"
> >     local size="$2"
> > -
> >     local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$fault_usage_file"
> > -  # Wait for hugetlbfs memory to get written.
> > -  while [ $(cat $path) != $size ]; do
> > -    echo Waiting for hugetlb memory to reach size $size.
> > -    cat $path
> > -    sleep 0.5
> > -  done
> > +
> > +  wait_for_file_value "$path" "$size"
> >   }
> >
> >   function write_hugetlbfs_and_get_usage() {
>
> wait_for_file_value() now return 0 onr success and 1 on timeout.
> However, none of the callers of the wait_for_hugetlb_memory* are
> checking their return values and acting accordingly. Are we expecting
> that the test will show failure because the waiting isn't completed or
> should we explicitly exit with ksft_fail (1) value?

Hmm, it seems the test shouldn't exit too early.

As the wait_for_hugetlb_memory* is only trying 60s to examine the file
value, if timeouted, we still need to keep going because the test requires
CLEANUP work and exit/report from there.

The key point of each subtest is to save the '$write_result' value and
examine it
which controls the whole test to exit.

e.g.

This is an intentional error test:

# ./charge_reserved_hugetlb.sh -cgroup-v2
CLEANUP DONE
...
Writing to this path: /mnt/huge/test
Writing this size: 2684354560
Not populating.
Not writing to memory.
Using method=0
Shared mapping.
RESERVE mapping.
Allocating using HUGETLBFS.
write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current
to become '2684354560' (current: '0') (try 1/60)
Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current
to become '2684354560' (current: '0') (try 2/60)
Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current
to become '2684354560' (current: '0') (try 3/60)
Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current
to become '2684354560' (current: '0') (try 4/60)
...
Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current
to become '2684354560' (current: '0') (try 60/60)
ERROR: timeout waiting for
/sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to
become '2684354560'
After write:
hugetlb_usage=0
reserved_usage=0
0
0
Memory charged to hugtlb=0
Memory charged to reservation=0
expected (2684354560) != actual (0): Reserved memory not charged to
reservation usage.
CLEANUP DONE


-- 
Regards,
Li Wang