Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=98b830d26095007aeb04041147b93d2b74e0a0c0
Commit:     98b830d26095007aeb04041147b93d2b74e0a0c0
Parent:     241651d04d672fb685b2874707016cbbf95931e5
Author:     Artem Bityutskiy <[EMAIL PROTECTED]>
AuthorDate: Tue Aug 28 20:33:32 2007 +0300
Committer:  David Woodhouse <[EMAIL PROTECTED]>
CommitDate: Thu Sep 6 10:16:22 2007 +0100

    [MTD] [NAND] 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.
    
    Caught-by: Adrian Hunter <[EMAIL PROTECTED]>
    Signed-off-by: Artem Bityutskiy <[EMAIL PROTECTED]>
    Signed-off-by: David Woodhouse <[EMAIL PROTECTED]>
---
 drivers/mtd/nand/nandsim.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/mtd/nand/nandsim.c b/drivers/mtd/nand/nandsim.c
index 205df0f..a757480 100644
--- a/drivers/mtd/nand/nandsim.c
+++ b/drivers/mtd/nand/nandsim.c
@@ -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;
-
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