This is a note to let you know that I've just added the patch titled
mm: hugetlb pages should not be reserved by shmat() if SHM_NORESERVE
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-hugetlb-pages-should-not-be-reserved-by-shmat-if-shm_noreserve.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e656c7a9e59607d1672d85ffa9a89031876ffe67 Mon Sep 17 00:00:00 2001
From: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
Date: Tue, 23 Jan 2024 12:04:42 -0800
Subject: mm: hugetlb pages should not be reserved by shmat() if SHM_NORESERVE
From: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
commit e656c7a9e59607d1672d85ffa9a89031876ffe67 upstream.
For shared memory of type SHM_HUGETLB, hugetlb pages are reserved in
shmget() call. If SHM_NORESERVE flags is specified then the hugetlb pages
are not reserved. However when the shared memory is attached with the
shmat() call the hugetlb pages are getting reserved incorrectly for
SHM_HUGETLB shared memory created with SHM_NORESERVE which is a bug.
-------------------------------
Following test shows the issue.
$cat shmhtb.c
int main()
{
int shmflags = 0660 | IPC_CREAT | SHM_HUGETLB | SHM_NORESERVE;
int shmid;
shmid = shmget(SKEY, SHMSZ, shmflags);
if (shmid < 0)
{
printf("shmat: shmget() failed, %d\n", errno);
return 1;
}
printf("After shmget()\n");
system("cat /proc/meminfo | grep -i hugepages_");
shmat(shmid, NULL, 0);
printf("\nAfter shmat()\n");
system("cat /proc/meminfo | grep -i hugepages_");
shmctl(shmid, IPC_RMID, NULL);
return 0;
}
#sysctl -w vm.nr_hugepages=20
#./shmhtb
After shmget()
HugePages_Total: 20
HugePages_Free: 20
HugePages_Rsvd: 0
HugePages_Surp: 0
After shmat()
HugePages_Total: 20
HugePages_Free: 20
HugePages_Rsvd: 5 <--
HugePages_Surp: 0
--------------------------------
Fix is to ensure that hugetlb pages are not reserved for SHM_HUGETLB shared
memory in the shmat() call.
Link: https://lkml.kernel.org/r/1706040282-12388-1-git-send-email-prakash.sangappa@xxxxxxxxxx
Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
Acked-by: Muchun Song <muchun.song@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -135,6 +135,7 @@ static int hugetlbfs_file_mmap(struct fi
loff_t len, vma_len;
int ret;
struct hstate *h = hstate_file(file);
+ vm_flags_t vm_flags;
/*
* vma address alignment (but not the pgoff alignment) has
@@ -176,10 +177,20 @@ static int hugetlbfs_file_mmap(struct fi
file_accessed(file);
ret = -ENOMEM;
+
+ vm_flags = vma->vm_flags;
+ /*
+ * for SHM_HUGETLB, the pages are reserved in the shmget() call so skip
+ * reserving here. Note: only for SHM hugetlbfs file, the inode
+ * flag S_PRIVATE is set.
+ */
+ if (inode->i_flags & S_PRIVATE)
+ vm_flags |= VM_NORESERVE;
+
if (!hugetlb_reserve_pages(inode,
vma->vm_pgoff >> huge_page_order(h),
len >> huge_page_shift(h), vma,
- vma->vm_flags))
+ vm_flags))
goto out;
ret = 0;
Patches currently in stable-queue which might be from prakash.sangappa@xxxxxxxxxx are
queue-5.15/mm-hugetlb-pages-should-not-be-reserved-by-shmat-if-shm_noreserve.patch
