This is a note to let you know that I've just added the patch titled s390/extmem: return correct segment type in __segment_load() 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: s390-extmem-return-correct-segment-type-in-__segment_load.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 8c42dd78df148c90e48efff204cce38743906a79 Mon Sep 17 00:00:00 2001 From: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> Date: Mon, 27 Feb 2023 20:03:00 +0100 Subject: s390/extmem: return correct segment type in __segment_load() From: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> commit 8c42dd78df148c90e48efff204cce38743906a79 upstream. Commit f05f62d04271f ("s390/vmem: get rid of memory segment list") reshuffled the call to vmem_add_mapping() in __segment_load(), which now overwrites rc after it was set to contain the segment type code. As result, __segment_load() will now always return 0 on success, which corresponds to the segment type code SEG_TYPE_SW, i.e. a writeable segment. This results in a kernel crash when loading a read-only segment as dcssblk block device, and trying to write to it. Instead of reshuffling code again, make sure to return the segment type on success, and also describe this rather delicate and unexpected logic in the function comment. Also initialize new segtype variable with invalid value, to prevent possible future confusion. Fixes: f05f62d04271 ("s390/vmem: get rid of memory segment list") Cc: <stable@xxxxxxxxxxxxxxx> # 5.9+ Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> Reviewed-by: Heiko Carstens <hca@xxxxxxxxxxxxx> Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/s390/mm/extmem.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) --- a/arch/s390/mm/extmem.c +++ b/arch/s390/mm/extmem.c @@ -289,15 +289,17 @@ segment_overlaps_others (struct dcss_seg /* * real segment loading function, called from segment_load + * Must return either an error code < 0, or the segment type code >= 0 */ static int __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long *end) { unsigned long start_addr, end_addr, dummy; struct dcss_segment *seg; - int rc, diag_cc; + int rc, diag_cc, segtype; start_addr = end_addr = 0; + segtype = -1; seg = kmalloc(sizeof(*seg), GFP_KERNEL | GFP_DMA); if (seg == NULL) { rc = -ENOMEM; @@ -326,9 +328,9 @@ __segment_load (char *name, int do_nonsh seg->res_name[8] = '\0'; strlcat(seg->res_name, " (DCSS)", sizeof(seg->res_name)); seg->res->name = seg->res_name; - rc = seg->vm_segtype; - if (rc == SEG_TYPE_SC || - ((rc == SEG_TYPE_SR || rc == SEG_TYPE_ER) && !do_nonshared)) + segtype = seg->vm_segtype; + if (segtype == SEG_TYPE_SC || + ((segtype == SEG_TYPE_SR || segtype == SEG_TYPE_ER) && !do_nonshared)) seg->res->flags |= IORESOURCE_READONLY; /* Check for overlapping resources before adding the mapping. */ @@ -386,7 +388,7 @@ __segment_load (char *name, int do_nonsh out_free: kfree(seg); out: - return rc; + return rc < 0 ? rc : segtype; } /* Patches currently in stable-queue which might be from gerald.schaefer@xxxxxxxxxxxxx are queue-5.15/s390-extmem-return-correct-segment-type-in-__segment_load.patch