The patch titled
Subject: fs/buffer.c: add debug print for __getblk_gfp() stall problem
has been added to the -mm tree. Its filename is
info-task-hung-in-generic_file_write_iter.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/info-task-hung-in-generic_file_write_iter.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/info-task-hung-in-generic_file_write_iter.patch
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------------------------------------------------------
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Subject: fs/buffer.c: add debug print for __getblk_gfp() stall problem
Among syzbot's unresolved hung task reports, 18 out of 65 reports contain
__getblk_gfp() line in the backtrace. Since there is a comment block that
says that __getblk_gfp() will lock up the machine if try_to_free_buffers()
attempt from grow_dev_page() is failing, let's start from checking whether
syzbot is hitting that case. This change will be removed after the bug is
fixed.
Link: http://lkml.kernel.org/r/9b9fcdda-c347-53ee-fdbb-8a7d11cf430e@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: <syzkaller-bugs@xxxxxxxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/buffer.c | 50 ++++++++++++++++++++++++++++++++++++++--
include/linux/sched.h | 7 +++++
lib/Kconfig.debug | 6 ++++
3 files changed, 61 insertions(+), 2 deletions(-)
diff -puN fs/buffer.c~info-task-hung-in-generic_file_write_iter fs/buffer.c
--- a/fs/buffer.c~info-task-hung-in-generic_file_write_iter
+++ a/fs/buffer.c
@@ -955,10 +955,20 @@ grow_dev_page(struct block_device *bdev,
end_block = init_page_buffers(page, bdev,
(sector_t)index << sizebits,
size);
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x01;
+#endif
goto done;
}
- if (!try_to_free_buffers(page))
+ if (!try_to_free_buffers(page)) {
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x02;
+#endif
goto failed;
+ }
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x04;
+#endif
}
/*
@@ -978,6 +988,9 @@ grow_dev_page(struct block_device *bdev,
spin_unlock(&inode->i_mapping->private_lock);
done:
ret = (block < end_block) ? 1 : -ENXIO;
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x08;
+#endif
failed:
unlock_page(page);
put_page(page);
@@ -1033,6 +1046,12 @@ __getblk_slow(struct block_device *bdev,
return NULL;
}
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_stamp = jiffies;
+ current->getblk_executed = 0;
+ current->getblk_bh_count = 0;
+ current->getblk_bh_state = 0;
+#endif
for (;;) {
struct buffer_head *bh;
int ret;
@@ -1044,6 +1063,18 @@ __getblk_slow(struct block_device *bdev,
ret = grow_buffers(bdev, block, size, gfp);
if (ret < 0)
return NULL;
+
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ if (!time_after(jiffies, current->getblk_stamp + 3 * HZ))
+ continue;
+ printk(KERN_ERR "%s(%u): getblk(): executed=%x bh_count=%d bh_state=%lx\n",
+ current->comm, current->pid, current->getblk_executed,
+ current->getblk_bh_count, current->getblk_bh_state);
+ current->getblk_executed = 0;
+ current->getblk_bh_count = 0;
+ current->getblk_bh_state = 0;
+ current->getblk_stamp = jiffies;
+#endif
}
}
@@ -3212,6 +3243,11 @@ EXPORT_SYMBOL(sync_dirty_buffer);
*/
static inline int buffer_busy(struct buffer_head *bh)
{
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x80;
+ current->getblk_bh_count = atomic_read(&bh->b_count);
+ current->getblk_bh_state = bh->b_state;
+#endif
return atomic_read(&bh->b_count) |
(bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
}
@@ -3250,11 +3286,18 @@ int try_to_free_buffers(struct page *pag
int ret = 0;
BUG_ON(!PageLocked(page));
- if (PageWriteback(page))
+ if (PageWriteback(page)) {
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x10;
+#endif
return 0;
+ }
if (mapping == NULL) { /* can this still happen? */
ret = drop_buffers(page, &buffers_to_free);
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x20;
+#endif
goto out;
}
@@ -3278,6 +3321,9 @@ int try_to_free_buffers(struct page *pag
if (ret)
cancel_dirty_page(page);
spin_unlock(&mapping->private_lock);
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ current->getblk_executed |= 0x40;
+#endif
out:
if (buffers_to_free) {
struct buffer_head *bh = buffers_to_free;
diff -puN include/linux/sched.h~info-task-hung-in-generic_file_write_iter include/linux/sched.h
--- a/include/linux/sched.h~info-task-hung-in-generic_file_write_iter
+++ a/include/linux/sched.h
@@ -1183,6 +1183,13 @@ struct task_struct {
void *security;
#endif
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+ unsigned long getblk_stamp;
+ unsigned int getblk_executed;
+ unsigned int getblk_bh_count;
+ unsigned long getblk_bh_state;
+#endif
+
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.
diff -puN lib/Kconfig.debug~info-task-hung-in-generic_file_write_iter lib/Kconfig.debug
--- a/lib/Kconfig.debug~info-task-hung-in-generic_file_write_iter
+++ a/lib/Kconfig.debug
@@ -2034,3 +2034,9 @@ config IO_STRICT_DEVMEM
if the driver using a given range cannot be disabled.
If in doubt, say Y.
+
+config DEBUG_AID_FOR_SYZBOT
+ bool "Additional debug code for syzbot"
+ default n
+ help
+ This option is intended for testing by syzbot.
_
Patches currently in -mm which might be from penguin-kernel@xxxxxxxxxxxxxxxxxxx are
dentry-fix-kmemcheck-splat-at-take_dentry_name_snapshot.patch
info-task-hung-in-generic_file_write_iter.patch
hfsplus-dont-return-0-when-fill_super-failed.patch
bfs-add-sanity-check-at-bfs_fill_super.patch
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