@@ -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,
@@ -1046,7 +1046,13 @@ register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
if (err && is_register)
goto free;
-
+ /*
+ * We take mmap_lock for writing to avoid the race with
+ * find_active_uprobe() which takes mmap_lock for reading.
+ * Thus this install_breakpoint() can not make
+ * is_trap_at_addr() true right after find_uprobe()
+ * returns NULL in find_active_uprobe().
+ */
mmap_write_lock(mm);
vma = find_vma(mm, info->vaddr);
if (!vma || !valid_vma(vma, is_register) ||
The comment above uprobe_write_opcode() is wrong, unapply_uprobe() calls it under mmap_read_lock() and this is correct. And it is completely unclear why register_for_each_vma() takes mmap_lock for writing, add a comment to explain that mmap_write_lock() is needed to avoid the following race: - A task T hits the bp installed by uprobe and calls find_active_uprobe() - uprobe_unregister() removes this uprobe/bp - T calls find_uprobe() which returns NULL - another uprobe_register() installs the bp at the same address - T calls is_trap_at_addr() which returns true - T returns to handle_swbp() and gets SIGTRAP. Reported-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- kernel/events/uprobes.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)