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Message-ID: <a4a7801d0904031738h68bf6218lfd3349ca50f46642@mail.gmail.com>
Date: Fri, 3 Apr 2009 17:38:33 -0700
From: Ying Han <yinghan@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: linux-ext4@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Ying Han <yinghan@...gle.com>,
Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] ext2: Fix data corruption for racing writes
On Thu, Apr 2, 2009 at 4:36 PM, Jan Kara <jack@...e.cz> wrote:
>
> If two writers allocating blocks to file race with each other (e.g. because
> writepages races with ordinary write or two writepages race with each other),
> ext2_getblock() can be called on the same inode in parallel. Before we are
> going to allocate new blocks, we have to recheck the block chain we have
> obtained so far without holding truncate_mutex. Otherwise we could overwrite
> the indirect block pointer set by the other writer leading to data loss.
>
> The below test program by Ying is able to reproduce the data loss with ext2
> on in BRD in a few minutes if the machine is under memory pressure:
>
> long kMemSize = 50 << 20;
> int kPageSize = 4096;
>
> int main(int argc, char **argv) {
> int status;
> int count = 0;
> int i;
> char *fname = "/mnt/test.mmap";
> char *mem;
> unlink(fname);
> int fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0600);
> status = ftruncate(fd, kMemSize);
> mem = mmap(0, kMemSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> // Fill the memory with 1s.
> memset(mem, 1, kMemSize);
> sleep(2);
> for (i = 0; i < kMemSize; i++) {
> int byte_good = mem[i] != 0;
> if (!byte_good && ((i % kPageSize) == 0)) {
> //printf("%d ", i / kPageSize);
> count++;
> }
> }
> munmap(mem, kMemSize);
> close(fd);
> unlink(fname);
>
> if (count > 0) {
> printf("Running %d bad page\n", count);
> return 1;
> }
> return 0;
> }
>
> CC: Ying Han <yinghan@...gle.com>
> CC: Nick Piggin <nickpiggin@...oo.com.au>
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
> fs/ext2/inode.c | 44 +++++++++++++++++++++++++++++++++-----------
> 1 files changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index b43b955..acf6788 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -590,9 +590,8 @@ static int ext2_get_blocks(struct inode *inode,
>
> if (depth == 0)
> return (err);
> -reread:
> - partial = ext2_get_branch(inode, depth, offsets, chain, &err);
>
> + partial = ext2_get_branch(inode, depth, offsets, chain, &err);
> /* Simplest case - block found, no allocation needed */
> if (!partial) {
> first_block = le32_to_cpu(chain[depth - 1].key);
> @@ -602,15 +601,16 @@ reread:
> while (count < maxblocks && count <= blocks_to_boundary) {
> ext2_fsblk_t blk;
>
> - if (!verify_chain(chain, partial)) {
> + if (!verify_chain(chain, chain + depth - 1)) {
> /*
> * Indirect block might be removed by
> * truncate while we were reading it.
> * Handling of that case: forget what we've
> * got now, go to reread.
> */
> + err = -EAGAIN;
> count = 0;
> - goto changed;
> + break;
> }
> blk = le32_to_cpu(*(chain[depth-1].p + count));
> if (blk == first_block + count)
> @@ -618,7 +618,8 @@ reread:
> else
> break;
> }
> - goto got_it;
> + if (err != -EAGAIN)
> + goto got_it;
> }
>
> /* Next simple case - plain lookup or failed read of indirect block */
> @@ -626,6 +627,33 @@ reread:
> goto cleanup;
>
> mutex_lock(&ei->truncate_mutex);
> + /*
> + * If the indirect block is missing while we are reading
> + * the chain(ext3_get_branch() returns -EAGAIN err), or
> + * if the chain has been changed after we grab the semaphore,
> + * (either because another process truncated this branch, or
> + * another get_block allocated this branch) re-grab the chain to see if
> + * the request block has been allocated or not.
> + *
> + * Since we already block the truncate/other get_block
> + * at this point, we will have the current copy of the chain when we
> + * splice the branch into the tree.
> + */
> + if (err == -EAGAIN || !verify_chain(chain, partial)) {
> + while (partial > chain) {
> + brelse(partial->bh);
> + partial--;
> + }
> + partial = ext2_get_branch(inode, depth, offsets, chain, &err);
> + if (!partial) {
> + count++;
> + mutex_unlock(&ei->truncate_mutex);
> + if (err)
> + goto cleanup;
> + clear_buffer_new(bh_result);
> + goto got_it;
> + }
> + }
>
> /*
> * Okay, we need to do block allocation. Lazily initialize the block
> @@ -683,12 +711,6 @@ cleanup:
> partial--;
> }
> return err;
> -changed:
> - while (partial > chain) {
> - brelse(partial->bh);
> - partial--;
> - }
> - goto reread;
> }
>
> int ext2_get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
I tried this patch and seems i got deadlock on the truncate_mutex.
Here is the message after enabling lockdep. I pasted the same message
on the origianal thread.
kernel: 1 lock held by kswapd1/264:
kernel: #0: (&ei->truncate_mutex){--..}, at: [<ffffffff8031d529>]
ext2_get_block+0x109/0x960
kernel: INFO: task ftruncate_mmap:2950 blocked for more than 120 seconds.
kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
this message.
kernel: ftruncate_mma D ffff81047e733a80 0 2950 2858
kernel: ffff8101798516f8 0000000000000092 0000000000000000 0000000000000046
kernel: ffff81047e0a1260 ffff81047f070000 ffff81047e0a15c0 0000000100130c66
kernel: 00000000ffffffff ffffffff8025740d 0000000000000000 0000000000000000
kernel: Call Trace:
kernel: [<ffffffff8025740d>] mark_held_locks+0x3d/0x80
kernel: [<ffffffff804d78bd>] mutex_lock_nested+0x14d/0x280
kernel: [<ffffffff804d7855>] mutex_lock_nested+0xe5/0x280
kernel: [<ffffffff8031d529>] ext2_get_block+0x109/0x960
kernel: [<ffffffff802ca2e3>] create_empty_buffers+0x43/0xb0
kernel: [<ffffffff802ca2e3>] create_empty_buffers+0x43/0xb0
kernel: [<ffffffff802ca217>] alloc_page_buffers+0x97/0x120
kernel: [<ffffffff802cbfb6>] __block_write_full_page+0x206/0x320
kernel: [<ffffffff802cbe70>] __block_write_full_page+0xc0/0x320
kernel: [<ffffffff8031d420>] ext2_get_block+0x0/0x960
kernel: [<ffffffff8027c74e>] shrink_page_list+0x4fe/0x650
kernel: [<ffffffff80257ee8>] __lock_acquire+0x3b8/0x1080
kernel: [<ffffffff8027be18>] isolate_lru_pages+0x88/0x230
kernel: [<ffffffff8027c9ea>] shrink_inactive_list+0x14a/0x3f0
kernel: [<ffffffff8027cd43>] shrink_zone+0xb3/0x130
kernel: [<ffffffff80249e90>] autoremove_wake_function+0x0/0x30
kernel: [<ffffffff8027d1a8>] try_to_free_pages+0x268/0x3e0
kernel: [<ffffffff8027bfc0>] isolate_pages_global+0x0/0x40
kernel: [<ffffffff802774f7>] __alloc_pages_internal+0x1d7/0x4a0
kernel: [<ffffffff80279b94>] __do_page_cache_readahead+0x124/0x270
kernel: [<ffffffff8027314f>] filemap_fault+0x18f/0x400
kernel: [<ffffffff80280925>] __do_fault+0x65/0x450
kernel: [<ffffffff80257ee8>] __lock_acquire+0x3b8/0x1080
kernel: [<ffffffff803475dd>] __down_read_trylock+0x1d/0x60
kernel: [<ffffffff8028389a>] handle_mm_fault+0x18a/0x7a0
kernel: [<ffffffff804dba1c>] do_page_fault+0x29c/0x930
kernel: [<ffffffff804d8b46>] trace_hardirqs_on_thunk+0x35/0x3a
kernel: [<ffffffff804d94dd>] error_exit+0x0/0xa9
kernel:
kernel: 2 locks held by ftruncate_mmap/2950:
kernel: #0: (&mm->mmap_sem){----}, at: [<ffffffff804db9af>]
do_page_fault+0x22f/0x930
kernel: #1: (&ei->truncate_mutex){--..}, at: [<ffffffff8031d529>]
ext2_get_block+0x109/0x960
Besides than that, does this patch fix the problem while moving the
mutex up to the beginning of ext_get_blocks() does too? Like the
following one
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 384fc0d..bef3ef7 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -586,11 +586,13 @@ static int ext2_get_blocks(struct inode *inode,
int count = 0;
ext2_fsblk_t first_block = 0;
+ mutex_lock(&ei->truncate_mutex);
depth = ext2_block_to_path(inode,iblock,offsets,&blocks_to_boundary);
- if (depth == 0)
+ if (depth == 0) {
+ mutex_unlock(&ei->truncate_mutex);
return (err);
-reread:
+ }
partial = ext2_get_branch(inode, depth, offsets, chain, &err);
/* Simplest case - block found, no allocation needed */
@@ -602,16 +604,6 @@ reread:
while (count < maxblocks && count <= blocks_to_boundary) {
ext2_fsblk_t blk;
- if (!verify_chain(chain, partial)) {
- /*
- * Indirect block might be removed by
- * truncate while we were reading it.
- * Handling of that case: forget what we've
- * got now, go to reread.
- */
- count = 0;
- goto changed;
- }
blk = le32_to_cpu(*(chain[depth-1].p + count));
if (blk == first_block + count)
count++;
@@ -625,7 +617,6 @@ reread:
if (!create || err == -EIO)
goto cleanup;
- mutex_lock(&ei->truncate_mutex);
/*
* Okay, we need to do block allocation. Lazily initialize the block
@@ -651,7 +642,6 @@ reread:
offsets + (partial - chain), partial);
if (err) {
- mutex_unlock(&ei->truncate_mutex);
goto cleanup;
}
@@ -662,13 +652,11 @@ reread:
err = ext2_clear_xip_target (inode,
le32_to_cpu(chain[depth-1].key));
if (err) {
- mutex_unlock(&ei->truncate_mutex);
goto cleanup;
}
}
ext2_splice_branch(inode, iblock, partial, indirect_blks, count);
- mutex_unlock(&ei->truncate_mutex);
set_buffer_new(bh_result);
got_it:
map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
@@ -678,17 +666,12 @@ got_it:
/* Clean up and exit */
partial = chain + depth - 1; /* the whole chain */
cleanup:
+ mutex_unlock(&ei->truncate_mutex);
while (partial > chain) {
brelse(partial->bh);
partial--;
}
return err;
-changed:
- while (partial > chain) {
- brelse(partial->bh);
- partial--;
- }
- goto reread;
}
int ext2_get_block(struct inode *inode, sector_t iblock, struct
buffer_head *bh_result, int create)
--Ying
>
> --
> 1.6.0.2
>
> --
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