[PATCH v2 02/12] uprobes: correct mmap_sem locking assumptions in uprobe_write_opcode()

Andrii Nakryiko
2024-07-01T22:39:45Z

It seems like uprobe_write_opcode() doesn't require writer locked
mmap_sem, any lock (reader or writer) should be sufficient. This was
established in a discussion in [0] and looking through existing code
seems to confirm that there is no need for write-locked mmap_sem.

Fix the comment to state this clearly.

[0] https://lore.kernel.org/linux-trace-kernel/20240625190748.GC14254@redhat.com/

Fixes: 29dedee0e693 ("uprobes: Add mem_cgroup_charge_anon() into uprobe_write_opcode()")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/events/uprobes.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 081821fd529a..f87049c08ee9 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -453,7 +453,7 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
* @vaddr: the virtual address to store the opcode.
* @opcode: opcode to be written at @vaddr.
*
- * Called with mm->mmap_lock held for write.
+ * Called with mm->mmap_lock held for read or write.
* Return 0 (success) or a negative errno.
*/
int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
--
2.43.0