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authorZhihao Cheng <chengzhihao1@huawei.com>2022-05-10 21:38:05 +0800
committerJens Axboe <axboe@kernel.dk>2022-05-19 06:29:41 -0600
commit68f4c6eba70df70a720188bce95c85570ddfcc87 (patch)
tree4fd6021890ac7b4108104efb8f4e0a9c732512b1
parent42226c989789d8da4af1de0c31070c96726d990c (diff)
fs-writeback: writeback_sb_inodes´╝ÜRecalculate 'wrote' according skipped pagesfor-5.19/writeback-2022-05-22for-5.19/writeback
Commit 505a666ee3fc ("writeback: plug writeback in wb_writeback() and writeback_inodes_wb()") has us holding a plug during wb_writeback, which may cause a potential ABBA dead lock: wb_writeback fat_file_fsync blk_start_plug(&plug) for (;;) { iter i-1: some reqs have been added into plug->mq_list // LOCK A iter i: progress = __writeback_inodes_wb(wb, work) . writeback_sb_inodes // fat's bdev . __writeback_single_inode . . generic_writepages . . __block_write_full_page . . . . __generic_file_fsync . . . . sync_inode_metadata . . . . writeback_single_inode . . . . __writeback_single_inode . . . . fat_write_inode . . . . __fat_write_inode . . . . sync_dirty_buffer // fat's bdev . . . . lock_buffer(bh) // LOCK B . . . . submit_bh . . . . blk_mq_get_tag // LOCK A . . . trylock_buffer(bh) // LOCK B . . . redirty_page_for_writepage . . . wbc->pages_skipped++ . . --wbc->nr_to_write . wrote += write_chunk - wbc.nr_to_write // wrote > 0 . requeue_inode . redirty_tail_locked if (progress) // progress > 0 continue; iter i+1: queue_io // similar process with iter i, infinite for-loop ! } blk_finish_plug(&plug) // flush plug won't be called Above process triggers a hungtask like: [ 399.044861] INFO: task bb:2607 blocked for more than 30 seconds. [ 399.046824] Not tainted 5.18.0-rc1-00005-gefae4d9eb6a2-dirty [ 399.051539] task:bb state:D stack: 0 pid: 2607 ppid: 2426 flags:0x00004000 [ 399.051556] Call Trace: [ 399.051570] __schedule+0x480/0x1050 [ 399.051592] schedule+0x92/0x1a0 [ 399.051602] io_schedule+0x22/0x50 [ 399.051613] blk_mq_get_tag+0x1d3/0x3c0 [ 399.051640] __blk_mq_alloc_requests+0x21d/0x3f0 [ 399.051657] blk_mq_submit_bio+0x68d/0xca0 [ 399.051674] __submit_bio+0x1b5/0x2d0 [ 399.051708] submit_bio_noacct+0x34e/0x720 [ 399.051718] submit_bio+0x3b/0x150 [ 399.051725] submit_bh_wbc+0x161/0x230 [ 399.051734] __sync_dirty_buffer+0xd1/0x420 [ 399.051744] sync_dirty_buffer+0x17/0x20 [ 399.051750] __fat_write_inode+0x289/0x310 [ 399.051766] fat_write_inode+0x2a/0xa0 [ 399.051783] __writeback_single_inode+0x53c/0x6f0 [ 399.051795] writeback_single_inode+0x145/0x200 [ 399.051803] sync_inode_metadata+0x45/0x70 [ 399.051856] __generic_file_fsync+0xa3/0x150 [ 399.051880] fat_file_fsync+0x1d/0x80 [ 399.051895] vfs_fsync_range+0x40/0xb0 [ 399.051929] __x64_sys_fsync+0x18/0x30 In my test, 'need_resched()' (which is imported by 590dca3a71 "fs-writeback: unplug before cond_resched in writeback_sb_inodes") in function 'writeback_sb_inodes()' seldom comes true, unless cond_resched() is deleted from write_cache_pages(). Fix it by correcting wrote number according number of skipped pages in writeback_sb_inodes(). Goto Link to find a reproducer. Link: https://bugzilla.kernel.org/show_bug.cgi?id=215837 Cc: stable@vger.kernel.org # v4.3 Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20220510133805.1988292-1-chengzhihao1@huawei.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--fs/fs-writeback.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1fae0196292a..a1074a26e784 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1779,11 +1779,12 @@ static long writeback_sb_inodes(struct super_block *sb,
};
unsigned long start_time = jiffies;
long write_chunk;
- long wrote = 0; /* count both pages and inodes */
+ long total_wrote = 0; /* count both pages and inodes */
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
struct bdi_writeback *tmp_wb;
+ long wrote;
if (inode->i_sb != sb) {
if (work->sb) {
@@ -1859,7 +1860,9 @@ static long writeback_sb_inodes(struct super_block *sb,
wbc_detach_inode(&wbc);
work->nr_pages -= write_chunk - wbc.nr_to_write;
- wrote += write_chunk - wbc.nr_to_write;
+ wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;
+ wrote = wrote < 0 ? 0 : wrote;
+ total_wrote += wrote;
if (need_resched()) {
/*
@@ -1881,7 +1884,7 @@ static long writeback_sb_inodes(struct super_block *sb,
tmp_wb = inode_to_wb_and_lock_list(inode);
spin_lock(&inode->i_lock);
if (!(inode->i_state & I_DIRTY_ALL))
- wrote++;
+ total_wrote++;
requeue_inode(inode, tmp_wb, &wbc);
inode_sync_complete(inode);
spin_unlock(&inode->i_lock);
@@ -1895,14 +1898,14 @@ static long writeback_sb_inodes(struct super_block *sb,
* bail out to wb_writeback() often enough to check
* background threshold and other termination conditions.
*/
- if (wrote) {
+ if (total_wrote) {
if (time_is_before_jiffies(start_time + HZ / 10UL))
break;
if (work->nr_pages <= 0)
break;
}
}
- return wrote;
+ return total_wrote;
}
static long __writeback_inodes_wb(struct bdi_writeback *wb,