On 2018-11-30 14:47:36 [-0800], Kees Cook wrote:
> diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
> index cfe87b465819..0f7d97917197 100644
> --- a/drivers/firmware/efi/efi-pstore.c
> +++ b/drivers/firmware/efi/efi-pstore.c
> @@ -259,8 +259,7 @@ static int efi_pstore_write(struct pstore_record *record)
> efi_name[i] = name[i];
>
> ret = efivar_entry_set_safe(efi_name, vendor, PSTORE_EFI_ATTRIBUTES,
> - !pstore_cannot_block_path(record->reason),
> - record->size, record->psi->buf);
> + preemptible(), record->size, record->psi->buf);
Well. Better I think.
might_sleep() / preempt_count_equals() checks for preemptible() + rcu_preempt_depth().
kmsg_dump() starts with rcu_read_lock() which means with this patch applied I
got:
| BUG: sleeping function called from invalid context at kernel/sched/completion.c:99
| in_atomic(): 0, irqs_disabled(): 0, pid: 2286, name: sig-xstate-bum PC: 0 RCU: 1
| Preemption disabled at:
| [<ffffffff9b959085>] __queue_work+0x95/0x440
| CPU: 30 PID: 2286 Comm: sig-xstate-bum Tainted: G D 4.20.0-rc3+ #90
| Call Trace:
| dump_stack+0x4f/0x6a
| ___might_sleep.cold.91+0xef/0x100
| __might_sleep+0x50/0x90
| wait_for_completion+0x32/0x130
| virt_efi_query_variable_info+0x14e/0x160
| efi_query_variable_store+0x51/0x1a0
| efivar_entry_set_safe+0xa3/0x1b0
| efi_pstore_write+0x110/0x140
| pstore_dump+0x114/0x320
| kmsg_dump+0xa4/0xd0
| oops_exit+0x7f/0x90
| oops_end+0x67/0xd0
| die+0x41/0x4a
| do_general_protection+0xc1/0x150
| general_protection+0x1e/0x30
| RIP: 0010:__fpu__restore_sig+0x1c1/0x540
just in case you wonder why both counter are zero and it still creates
this backtrace.
> if (record->reason == KMSG_DUMP_OOPS)
> efivar_run_worker();
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 2387cb74f729..afdfd3687f94 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -400,23 +401,20 @@ static void pstore_dump(struct kmsg_dumper *dumper,
> unsigned long total = 0;
> const char *why;
> unsigned int part = 1;
> - unsigned long flags = 0;
> - int is_locked;
> int ret;
>
> why = get_reason_str(reason);
>
> - if (pstore_cannot_block_path(reason)) {
> - is_locked = spin_trylock_irqsave(&psinfo->buf_lock, flags);
> - if (!is_locked) {
> - pr_err("pstore dump routine blocked in %s path, may corrupt error record\n"
> - , in_nmi() ? "NMI" : why);
> + if (down_trylock(&psinfo->buf_lock)) {
> + /* Failed to acquire lock: give up if we cannot wait. */
> + if (pstore_cannot_wait(reason)) {
> + pr_err("dump skipped in %s path: may corrupt error record\n",
> + in_nmi() ? "NMI" : why);
> return;
> }
> - } else {
> - spin_lock_irqsave(&psinfo->buf_lock, flags);
> - is_locked = 1;
> + down_interruptible(&psinfo->buf_lock);
In function ‘pstore_dump’:
fs/pstore/platform.c:393:3: warning: ignoring return value of ‘down_interruptible’, declared with attribute warn_unused_result [-Wunused-result]
down_interruptible(&psinfo->buf_lock);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> }
Sebastian
