MTD: nandsim: avoid deadlocking FS

From: Artem Bityutskiy <[email protected]>
Date: Tue, 28 Aug 2007 20:33:32 +0300
Subject: [PATCH] MTD: nandsim: avoid deadlocking FS

Make nandsim use GFP_NOFS when allocating memory, because it might be used by a file-system (e.g. UBIFS2) which means, if we are short of memory, we may deadlock. Indee, UBIFS is holding a lock, writes to the media, reaches this place in NANDsim, kmalloc does not find the requested amount of RAM, calls memory shrinker, which decides to writeback inodes, calls FS, and it deadlocks on the lock which is already being held. Below is the UBIFS backtrace which demonstrates that:

[<c03717dc>] __mutex_lock_slowpath+0xc8/0x2e6
[<c0371a16>] mutex_lock+0x1c/0x1f
[<f8b9d076>] reserve_space+0x3d/0xa9 [ubifs]
[<f8b9d1bd>] make_one_reservation+0x2b/0x86 [ubifs]
[<f8b9d3fc>] ubifs_jrn_write_block+0xda/0x12f [ubifs]
[<f8b9ff3a>] ubifs_writepage+0x11d/0x1ec [ubifs]
[<c015d6ab>] shrink_inactive_list+0x7fa/0x969
[<c015d8c8>] shrink_zone+0xae/0x10c
[<c015e3b4>] try_to_free_pages+0x159/0x251
[<c015980a>] __alloc_pages+0x125/0x2f0
[<c016ff6a>] cache_alloc_refill+0x380/0x6ba
[<c01703f3>] __kmalloc+0x14f/0x157
[<f885722a>] do_state_action+0xab7/0xc74 [nandsim]
[<f885760c>] switch_state+0x225/0x402 [nandsim]
[<f8857e7e>] ns_hwcontrol+0x3e2/0x620 [nandsim]
[<f8862f53>] nand_command+0x2e/0x1a5 [nand]
[<f8861ad8>] nand_write_page+0x4a/0x9a [nand]
[<f88617b4>] nand_do_write_ops+0x1cf/0x343 [nand]
[<f8861a70>] nand_write+0x88/0xa6 [nand]
[<f8850b0e>] part_write+0x72/0x8b [mtd]
[<f88e19c5>] ubi_io_write+0x189/0x29c [ubi]
[<f88dfb98>] ubi_eba_write_leb+0xb6/0x699 [ubi]
[<f88def93>] ubi_leb_write+0xe4/0xe9 [ubi]
[<f8ba3b82>] ubifs_wbuf_write_nolock+0x333/0x4c9 [ubifs]
[<f8b9d28c>] write_node+0x74/0x8e [ubifs]
[<f8b9d422>] ubifs_jrn_write_block+0x100/0x12f [ubifs]
[<f8b9ff3a>] ubifs_writepage+0x11d/0x1ec [ubifs]
[<c0159e5b>] __writepage+0xb/0x26
[<c015a318>] write_cache_pages+0x203/0x2d9
[<c015a411>] generic_writepages+0x23/0x2d
[<c015a452>] do_writepages+0x37/0x39
[<c018e24a>] __writeback_single_inode+0x96/0x399
[<c018e903>] sync_sb_inodes+0x1a3/0x274
[<c018ebf3>] writeback_inodes+0xa6/0xd8
[<c015a9dd>] background_writeout+0x86/0x9e
[<c015ae9c>] pdflush+0xfb/0x1b6
[<c01387d7>] kthread+0x37/0x59
[<c0104dc3>] kernel_thread_helper+0x7/0x14

The deadlock is funny because it starts in pdflush/writeback, and comes back to writeback, then deadlocks. It seems we should look carefully for other places in UBI and MTD and use GFP_NOFS instead of GFP_KERNEL.

---
 drivers/mtd/nand/nandsim.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

index 205df0f..0b1823c 100644
@@ -1272,7 +1272,13 @@ static int prog_page(struct nandsim *ns, int num)
 	mypage = NS_GET_PAGE(ns);
 	if (mypage->byte == NULL) {
 		NS_DBG("prog_page: allocating page %d\n", ns->regs.row);
-		mypage->byte = kmalloc(ns->geom.pgszoob, GFP_KERNEL);
+		/*
+		 * We allocate memory with GFP_NOFS because a flash FS may
+		 * utilize this. If it is holding an FS lock, then gets here,
+		 * then kmalloc runs writeback which goes to the FS again
+		 * and deadlocks. This was seen in practice.
+		 */
+		mypage->byte = kmalloc(ns->geom.pgszoob, GFP_NOFS);
 		if (mypage->byte == NULL) {
 			NS_ERR("prog_page: error allocating memory for page %d\n", ns->regs.row);
 			return -1;

1.5.0.6

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)

Oh sorry, it is UBIFS, we do not have plans for UBIFS2 yet. Uhh, nasty typo!

Best regards,
Artem Bityutskiy (Битюцкий Артём)