Patch "mmc: core: fix race condition in mmc_wait_data_done" has been added to the 4.2-stable tree
Subsystems (2)
This is a note to let you know that I've just added the patch titled
mmc: core: fix race condition in mmc_wait_data_done
to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mmc-core-fix-race-condition-in-mmc_wait_data_done.patch
and it can be found in the queue-4.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
Quoted 1 line
From
71f8a4b81d040b3d094424197ca2f1bf811b1245Mon Sep 17 00:00:00 2001
From: Jialing Fu <[email protected]>
Date: Fri, 28 Aug 2015 11:13:09 +0800
Subject: mmc: core: fix race condition in mmc_wait_data_done
From: Jialing Fu <[email protected]>
commit 71f8a4b81d040b3d094424197ca2f1bf811b1245 upstream.
The following panic is captured in ker3.14, but the issue still exists in latest kernel.
---------------------------------------------------------------------
[ 20.738217] c0 3136 (Compiler) Unable to handle kernel NULL pointer dereference at virtual address 00000578 ...... [ 20.738499] c0 3136 (Compiler) PC is at _raw_spin_lock_irqsave+0x24/0x60 [ 20.738527] c0 3136 (Compiler) LR is at _raw_spin_lock_irqsave+0x20/0x60 [ 20.740134] c0 3136 (Compiler) Call trace: [ 20.740165] c0 3136 (Compiler) [<ffffffc0008ee900>] _raw_spin_lock_irqsave+0x24/0x60 [ 20.740200] c0 3136 (Compiler) [<ffffffc0000dd024>] __wake_up+0x1c/0x54 [ 20.740230] c0 3136 (Compiler) [<ffffffc000639414>] mmc_wait_data_done+0x28/0x34 [ 20.740262] c0 3136 (Compiler) [<ffffffc0006391a0>] mmc_request_done+0xa4/0x220 [ 20.740314] c0 3136 (Compiler) [<ffffffc000656894>] sdhci_tasklet_finish+0xac/0x264 [ 20.740352] c0 3136 (Compiler) [<ffffffc0000a2b58>] tasklet_action+0xa0/0x158 [ 20.740382] c0 3136 (Compiler) [<ffffffc0000a2078>] __do_softirq+0x10c/0x2e4 [ 20.740411] c0 3136 (Compiler) [<ffffffc0000a24bc>] irq_exit+0x8c/0xc0 [ 20.740439] c0 3136 (Compiler) [<ffffffc00008489c>] handle_IRQ+0x48/0xac [ 20.740469] c0 3136 (Compiler) [<ffffffc000081428>] gic_handle_irq+0x38/0x7c
----------------------------------------------------------------------
Because in SMP, "mrq" has race condition between below two paths:
path1: CPU0: <tasklet context>
static void mmc_wait_data_done(struct mmc_request *mrq)
{
mrq->host->context_info.is_done_rcv = true;
//
// If CPU0 has just finished "is_done_rcv = true" in path1, and at
// this moment, IRQ or ICache line missing happens in CPU0.
// What happens in CPU1 (path2)?
//
// If the mmcqd thread in CPU1(path2) hasn't entered to sleep mode:
// path2 would have chance to break from wait_event_interruptible
// in mmc_wait_for_data_req_done and continue to run for next
// mmc_request (mmc_blk_rw_rq_prep).
//
// Within mmc_blk_rq_prep, mrq is cleared to 0.
// If below line still gets host from "mrq" as the result of
// compiler, the panic happens as we traced.
wake_up_interruptible(&mrq->host->context_info.wait);}
path2: CPU1: <The mmcqd thread runs mmc_queue_thread>
static int mmc_wait_for_data_req_done(...
{
...
while (1) {
wait_event_interruptible(context_info->wait,
(context_info->is_done_rcv ||
context_info->is_new_req));
static void mmc_blk_rw_rq_prep(...
{
...
memset(brq, 0, sizeof(struct mmc_blk_request));This issue happens very coincidentally; however adding mdelay(1) in mmc_wait_data_done as below could duplicate it easily.
static void mmc_wait_data_done(struct mmc_request *mrq)
{
mrq->host->context_info.is_done_rcv = true;
+ mdelay(1);
wake_up_interruptible(&mrq->host->context_info.wait);
}At runtime, IRQ or ICache line missing may just happen at the same place of the mdelay(1).
This patch gets the mmc_context_info at the beginning of function, it can avoid this race condition.
--- drivers/mmc/core/core.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
drivers/mmc/core/core.c +4 -2
@@ -358,8 +358,10 @@ EXPORT_SYMBOL(mmc_start_bkops);*/ static void mmc_wait_data_done (struct mmc_request *mrq) { - mrq->host->context_info.is_done_rcv = true; -wake_up_interruptible (&mrq->host->context_info.wait); +struct mmc_context_info *context_info = &mrq->host->context_info; + + context_info->is_done_rcv = true; +wake_up_interruptible (&context_info->wait); }static void mmc_wait_done (struct mmc_request *mrq)
Patches currently in stable-queue which might be from [email protected] are
queue-4.2/mmc-core-fix-race-condition-in-mmc_wait_data_done.patch