On 29. 01. 24, 18:02, Greg Kroah-Hartman wrote:
6.7-stable review patch. If anyone has any objections, please let me know.
From: Charan Teja Kalla quic_charante@quicinc.com
commit 5ec8e8ea8b7783fab150cf86404fc38cb4db8800 upstream.
Hi,
our machinery (git-fixes) says, this is needed as a fix: commit f6564fce256a3944aa1bc76cb3c40e792d97c1eb Author: Marco Elver elver@google.com Date: Thu Jan 18 11:59:14 2024 +0100
mm, kmsan: fix infinite recursion due to RCU critical section
Leaving up to the recipients to decide, as I have no idea…
The below race is observed on a PFN which falls into the device memory region with the system memory configuration where PFN's are such that [ZONE_NORMAL ZONE_DEVICE ZONE_NORMAL]. Since normal zone start and end pfn contains the device memory PFN's as well, the compaction triggered will try on the device memory PFN's too though they end up in NOP(because pfn_to_online_page() returns NULL for ZONE_DEVICE memory sections). When from other core, the section mappings are being removed for the ZONE_DEVICE region, that the PFN in question belongs to, on which compaction is currently being operated is resulting into the kernel crash with CONFIG_SPASEMEM_VMEMAP enabled. The crash logs can be seen at [1].
compact_zone() memunmap_pages
__pageblock_pfn_to_page ...... (a)pfn_valid(): valid_section()//return true (b)__remove_pages()-> sparse_remove_section()-> section_deactivate(): [Free the array ms->usage and set ms->usage = NULL] pfn_section_valid() [Access ms->usage which is NULL]
NOTE: From the above it can be said that the race is reduced to between the pfn_valid()/pfn_section_valid() and the section deactivate with SPASEMEM_VMEMAP enabled.
The commit b943f045a9af("mm/sparse: fix kernel crash with pfn_section_valid check") tried to address the same problem by clearing the SECTION_HAS_MEM_MAP with the expectation of valid_section() returns false thus ms->usage is not accessed.
Fix this issue by the below steps:
a) Clear SECTION_HAS_MEM_MAP before freeing the ->usage.
b) RCU protected read side critical section will either return NULL when SECTION_HAS_MEM_MAP is cleared or can successfully access ->usage.
c) Free the ->usage with kfree_rcu() and set ms->usage = NULL. No attempt will be made to access ->usage after this as the SECTION_HAS_MEM_MAP is cleared thus valid_section() return false.
Thanks to David/Pavan for their inputs on this patch.
[1] https://lore.kernel.org/linux-mm/994410bb-89aa-d987-1f50-f514903c55aa@quicin...
On Snapdragon SoC, with the mentioned memory configuration of PFN's as [ZONE_NORMAL ZONE_DEVICE ZONE_NORMAL], we are able to see bunch of issues daily while testing on a device farm.
For this particular issue below is the log. Though the below log is not directly pointing to the pfn_section_valid(){ ms->usage;}, when we loaded this dump on T32 lauterbach tool, it is pointing.
...
thanks,