The patch titled Subject: mm: fix move/migrate_pages() race on task struct has been added to the -mm tree. Its filename is mm-fix-move-migrate_pages-race-on-task-struct.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Christoph Lameter <cl@xxxxxxxxx> Subject: mm: fix move/migrate_pages() race on task struct Migration functions perform the rcu_read_unlock too early. As a result the task pointed to may change from under us. The following patch extend the period of the rcu_read_lock until after the permissions checks are done. We also take a refcount so that the task reference is stable when calling security check functions and performing cpuset node validation (which takes a mutex). The refcount is dropped before actual page migration occurs so there is no change to the refcounts held during page migration. Also move the determination of the mm of the task struct to immediately before the do_migrate*() calls so that it is clear that we switch from handling the task during permission checks to the mm for the actual migration. Since the determination is only done once and we then no longer use the task_struct we can be sure that we operate on a specific address space that will not change from under us. Signed-off-by: Christoph Lameter <cl@xxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> Cc: Mel Gorman <mel@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mempolicy.c | 32 +++++++++++++++++++------------- mm/migrate.c | 36 +++++++++++++++++++----------------- 2 files changed, 38 insertions(+), 30 deletions(-) diff -puN mm/mempolicy.c~fix-move-migrate_pages-race-on-task-struct mm/mempolicy.c --- a/mm/mempolicy.c~fix-move-migrate_pages-race-on-task-struct +++ a/mm/mempolicy.c @@ -1322,12 +1322,9 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pi err = -ESRCH; goto out; } - mm = get_task_mm(task); - rcu_read_unlock(); + get_task_struct(task); err = -EINVAL; - if (!mm) - goto out; /* * Check if this process has the right to modify the specified @@ -1335,14 +1332,13 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pi * capabilities, superuser privileges or the same * userid as the target process. */ - rcu_read_lock(); tcred = __task_cred(task); if (cred->euid != tcred->suid && cred->euid != tcred->uid && cred->uid != tcred->suid && cred->uid != tcred->uid && !capable(CAP_SYS_NICE)) { rcu_read_unlock(); err = -EPERM; - goto out; + goto out_put; } rcu_read_unlock(); @@ -1350,26 +1346,36 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pi /* Is the user allowed to access the target nodes? */ if (!nodes_subset(*new, task_nodes) && !capable(CAP_SYS_NICE)) { err = -EPERM; - goto out; + goto out_put; } if (!nodes_subset(*new, node_states[N_HIGH_MEMORY])) { err = -EINVAL; - goto out; + goto out_put; } err = security_task_movememory(task); if (err) - goto out; + goto out_put; - err = do_migrate_pages(mm, old, new, - capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE); -out: + mm = get_task_mm(task); + put_task_struct(task); if (mm) - mmput(mm); + err = do_migrate_pages(mm, old, new, + capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE); + else + err = -EINVAL; + + mmput(mm); +out: NODEMASK_SCRATCH_FREE(scratch); return err; + +out_put: + put_task_struct(task); + goto out; + } diff -puN mm/migrate.c~fix-move-migrate_pages-race-on-task-struct mm/migrate.c --- a/mm/migrate.c~fix-move-migrate_pages-race-on-task-struct +++ a/mm/migrate.c @@ -1176,20 +1176,17 @@ set_status: * Migrate an array of page address onto an array of nodes and fill * the corresponding array of status. */ -static int do_pages_move(struct mm_struct *mm, struct task_struct *task, +static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, unsigned long nr_pages, const void __user * __user *pages, const int __user *nodes, int __user *status, int flags) { struct page_to_node *pm; - nodemask_t task_nodes; unsigned long chunk_nr_pages; unsigned long chunk_start; int err; - task_nodes = cpuset_mems_allowed(task); - err = -ENOMEM; pm = (struct page_to_node *)__get_free_page(GFP_KERNEL); if (!pm) @@ -1351,6 +1348,7 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, struct task_struct *task; struct mm_struct *mm; int err; + nodemask_t task_nodes; /* Check flags */ if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL)) @@ -1366,11 +1364,7 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, rcu_read_unlock(); return -ESRCH; } - mm = get_task_mm(task); - rcu_read_unlock(); - - if (!mm) - return -EINVAL; + get_task_struct(task); /* * Check if this process has the right to modify the specified @@ -1378,7 +1372,6 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, * capabilities, superuser privileges or the same * userid as the target process. */ - rcu_read_lock(); tcred = __task_cred(task); if (cred->euid != tcred->suid && cred->euid != tcred->uid && cred->uid != tcred->suid && cred->uid != tcred->uid && @@ -1393,16 +1386,25 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, if (err) goto out; - if (nodes) { - err = do_pages_move(mm, task, nr_pages, pages, nodes, status, - flags); - } else { - err = do_pages_stat(mm, nr_pages, pages, status); - } + task_nodes = cpuset_mems_allowed(task); + mm = get_task_mm(task); + put_task_struct(task); + + if (mm) { + if (nodes) + err = do_pages_move(mm, task_nodes, nr_pages, pages, nodes, + status, flags); + else + err = do_pages_stat(mm, nr_pages, pages, status); + } else + err = -EINVAL; -out: mmput(mm); return err; + +out: + put_task_struct(task); + return err; } /* _ Subject: Subject: mm: fix move/migrate_pages() race on task struct Patches currently in -mm which might be from cl@xxxxxxxxx are linux-next.patch mm-vmscan-forcibly-scan-highmem-if-there-are-too-many-buffer_heads-pinning-highmem.patch mm-fix-move-migrate_pages-race-on-task-struct.patch smp-introduce-a-generic-on_each_cpu_mask-function.patch slub-only-ipi-cpus-that-have-per-cpu-obj-to-flush.patch mm-only-ipi-cpus-to-drain-local-pages-if-they-exist.patch selftests-launch-individual-selftests-from-the-main-makefile.patch move-page-typesc-from-documentation-to-tools-vm.patch move-slabinfoc-to-tools-vm.patch move-hugepage-test-examples-to-tools-testing-selftests-vm.patch move-hugepage-test-examples-to-tools-testing-selftests-vm-fix.patch move-hugepage-test-examples-to-tools-testing-selftests-vm-fix-fix.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html