Re: processes stuck in llseek
From: David Sterba <hidden>
Date: 2011-08-16 12:36:18
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On Mon, Aug 15, 2011 at 11:59:50PM -0400, Dan Merillat wrote:
I noticed a series of hung_task notifications in dmesg, so I went poking at it. Process is 'dropbox', and it's stuck trying to llseek it's library.zip file.
looks like mutex lock is waiting, in btrfs_file_llseek. somebody else is holding it for that file. it could be a forgotten unlock (of inode->i_mutex) on some error path, but this does not look very promising to me, or the process holding the lock still exists and will be visible in process listings. locdep would tell more exactly.
strace of dropbox:
...
stat("/home/x/.dropbox-dist/library.zip", {st_mode=S_IFREG|0755,
st_size=11575179, ...}) = 0
open("/home/x/.dropbox-dist/library.zip", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0755, st_size=11575179, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x7fa766ea8000
fstat(3, {st_mode=S_IFREG|0755, st_size=11575179, ...}) = 0
lseek(3, 11571200, SEEK_SET
SEEK_SET is less than st_size
strace of dd if=library.zip of=/dev/null bs=1 seek=11571200:
open("library.zip", O_RDONLY) = 3
dup2(3, 0) = 0
close(3) = 0
lseek(0, 0, SEEK_CUR
[72960.716080] INFO: task dropbox:1348 blocked for more than 120 seconds.
[72960.716084] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[72960.716087] dropbox D ffff8800762d8a78 0 1348 1 0x00000004
[72960.716092] ffff880069cede18 0000000000000086 0000000000096000
0000000000000000
[72960.716097] ffff880069cec000 00000000000119c0 ffff8800762d8700
00000000000119c0
[72960.716101] ffff880069cedfd8 0000000000004000 ffff880069cedfd8
00000000000119c0
[72960.716106] Call Trace:
[72960.716113] [<ffffffff81331f9e>] ? trace_hardirqs_on_thunk+0x3a/0x3c
[72960.716119] [<ffffffff8155710a>] ? retint_restore_args+0xe/0xe
[72960.716124] [<ffffffff810e8ef1>] ? noop_llseek+0xa/0xa
[72960.716129] [<ffffffff810340ff>] ? mutex_spin_on_owner+0x1c/0x45
[72960.716133] [<ffffffff81555be0>] __mutex_lock_slowpath+0xd2/0x116
[72960.716137] [<ffffffff81559edd>] ? do_page_fault+0x374/0x3e6
[72960.716140] [<ffffffff81555a87>] mutex_lock+0x16/0x27
[72960.716146] [<ffffffff812c8ad7>] btrfs_file_llseek+0x38/0x297
[72960.716150] [<ffffffff81331fda>] ? trace_hardirqs_off_thunk+0x3a/0x6c
[72960.716153] [<ffffffff810e8f2c>] vfs_llseek+0x2e/0x30
[72960.716155] [<ffffffff810e9311>] sys_lseek+0x3e/0x5d
[72960.716159] [<ffffffff8155d4fb>] system_call_fastpath+0x16/0x1bjust a guess, as it touches file pages, can you try Sage's fix "truncate pages from clone ioctl target range" https://patchwork.kernel.org/patch/1054552/ under assumption that the file on which seek is run has been reflinked or at least written to during the running transaction (ie no sync in between).
Oddly enough, it's just llseek. I can copy/read the file sequentially just fine, but llseek fails on a copy as well.
incorrect or unexpected contents of the same-aged files would point to the missing truncate. david
quoted hunk ↗ jump to hunk
Once I get physically to the system I'll recompile to an unmodified kernel and try again. Other files of the same approximate age llseek correctly. Kernel is 3.1-rc1 with the fglrx module from AMD and the following patch: (I was playing with cross-subvolume reflinking, but not on this file)diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 7cf0133..a13b5e2 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c@@ -2182,7 +2182,7 @@ static noinline long btrfs_ioctl_clone(structfile *file, unsigned long srcfd, goto out_fput; ret = -EXDEV; - if (src->i_sb != inode->i_sb || BTRFS_I(src)->root != root) + if (src->i_sb != inode->i_sb) goto out_fput; ret = -ENOMEM;@@ -2246,13 +2246,13 @@ static noinline long btrfs_ioctl_clone(structfile *file, unsigned long srcfd, * note the key will change type as we walk through the * tree. */ - ret = btrfs_search_slot(NULL, root, &key, path, 0, 0); + ret = btrfs_search_slot(NULL, BTRFS_I(src)->root, &key, path, 0, 0); if (ret < 0) goto out; nritems = btrfs_header_nritems(path->nodes[0]); if (path->slots[0] >= nritems) { - ret = btrfs_next_leaf(root, path); + ret = btrfs_next_leaf(BTRFS_I(src)->root, path); if (ret < 0) goto out; if (ret > 0)@@ -2313,7 +2313,7 @@ static noinline long btrfs_ioctl_clone(structfile *file, unsigned long srcfd, else new_key.offset = destoff; - trans = btrfs_start_transaction(root, 1); + trans = btrfs_start_transaction(root, 3); if (IS_ERR(trans)) { ret = PTR_ERR(trans); goto out; -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html