From 54ea8e48a290ef368d0e3bd369f38ac4037a149f Mon Sep 17 00:00:00 2001 From: =?utf8?q?Arkadiusz=20Mi=C5=9Bkiewicz?= Date: Sat, 9 Aug 2014 00:11:17 +0200 Subject: [PATCH] - xfs hang fix --- kernel-small_fixes.patch | 138 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 138 insertions(+) diff --git a/kernel-small_fixes.patch b/kernel-small_fixes.patch index c64eee19..6199b0ae 100644 --- a/kernel-small_fixes.patch +++ b/kernel-small_fixes.patch @@ -113,3 +113,141 @@ index 4e565c8..732648b 100644 -- cgit v0.10.1 +commit 110dc24ad2ae4e9b94b08632fe1eb2fcdff83045 +Author: Dave Chinner +Date: Tue May 20 08:18:09 2014 +1000 + + xfs: log vector rounding leaks log space + + The addition of direct formatting of log items into the CIL + linear buffer added alignment restrictions that the start of each + vector needed to be 64 bit aligned. Hence padding was added in + xlog_finish_iovec() to round up the vector length to ensure the next + vector started with the correct alignment. + + This adds a small number of bytes to the size of + the linear buffer that is otherwise unused. The issue is that we + then use the linear buffer size to determine the log space used by + the log item, and this includes the unused space. Hence when we + account for space used by the log item, it's more than is actually + written into the iclogs, and hence we slowly leak this space. + + This results on log hangs when reserving space, with threads getting + stuck with these stack traces: + + Call Trace: + [] schedule+0x29/0x70 + [] xlog_grant_head_wait+0xa2/0x1a0 + [] xlog_grant_head_check+0xbd/0x140 + [] xfs_log_reserve+0x103/0x220 + [] xfs_trans_reserve+0x2f5/0x310 + ..... + + The 4 bytes is significant. Brain Foster did all the hard work in + tracking down a reproducable leak to inode chunk allocation (it went + away with the ikeep mount option). His rough numbers were that + creating 50,000 inodes leaked 11 log blocks. This turns out to be + roughly 800 inode chunks or 1600 inode cluster buffers. That + works out at roughly 4 bytes per cluster buffer logged, and at that + I started looking for a 4 byte leak in the buffer logging code. + + What I found was that a struct xfs_buf_log_format structure for an + inode cluster buffer is 28 bytes in length. This gets rounded up to + 32 bytes, but the vector length remains 28 bytes. Hence the CIL + ticket reservation is decremented by 32 bytes (via lv->lv_buf_len) + for that vector rather than 28 bytes which are written into the log. + + The fix for this problem is to separately track the bytes used by + the log vectors in the item and use that instead of the buffer + length when accounting for the log space that will be used by the + formatted log item. + + Again, thanks to Brian Foster for doing all the hard work and long + hours to isolate this leak and make finding the bug relatively + simple. + + Signed-off-by: Dave Chinner + Reviewed-by: Christoph Hellwig + Reviewed-by: Brian Foster + Signed-off-by: Dave Chinner + +diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h +index 2c40044..84e0deb 100644 +--- a/fs/xfs/xfs_log.h ++++ b/fs/xfs/xfs_log.h +@@ -24,7 +24,8 @@ struct xfs_log_vec { + struct xfs_log_iovec *lv_iovecp; /* iovec array */ + struct xfs_log_item *lv_item; /* owner */ + char *lv_buf; /* formatted buffer */ +- int lv_buf_len; /* size of formatted buffer */ ++ int lv_bytes; /* accounted space in buffer */ ++ int lv_buf_len; /* aligned size of buffer */ + int lv_size; /* size of allocated lv */ + }; + +@@ -52,15 +53,21 @@ xlog_prepare_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp, + return vec->i_addr; + } + ++/* ++ * We need to make sure the next buffer is naturally aligned for the biggest ++ * basic data type we put into it. We already accounted for this padding when ++ * sizing the buffer. ++ * ++ * However, this padding does not get written into the log, and hence we have to ++ * track the space used by the log vectors separately to prevent log space hangs ++ * due to inaccurate accounting (i.e. a leak) of the used log space through the ++ * CIL context ticket. ++ */ + static inline void + xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec, int len) + { +- /* +- * We need to make sure the next buffer is naturally aligned for the +- * biggest basic data type we put into it. We already accounted for +- * this when sizing the buffer. +- */ + lv->lv_buf_len += round_up(len, sizeof(uint64_t)); ++ lv->lv_bytes += len; + vec->i_len = len; + } + +diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c +index 7e54553..de835da 100644 +--- a/fs/xfs/xfs_log_cil.c ++++ b/fs/xfs/xfs_log_cil.c +@@ -97,7 +97,7 @@ xfs_cil_prepare_item( + { + /* Account for the new LV being passed in */ + if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED) { +- *diff_len += lv->lv_buf_len; ++ *diff_len += lv->lv_bytes; + *diff_iovecs += lv->lv_niovecs; + } + +@@ -111,7 +111,7 @@ xfs_cil_prepare_item( + else if (old_lv != lv) { + ASSERT(lv->lv_buf_len != XFS_LOG_VEC_ORDERED); + +- *diff_len -= old_lv->lv_buf_len; ++ *diff_len -= old_lv->lv_bytes; + *diff_iovecs -= old_lv->lv_niovecs; + kmem_free(old_lv); + } +@@ -239,7 +239,7 @@ xlog_cil_insert_format_items( + * that the space reservation accounting is correct. + */ + *diff_iovecs -= lv->lv_niovecs; +- *diff_len -= lv->lv_buf_len; ++ *diff_len -= lv->lv_bytes; + } else { + /* allocate new data chunk */ + lv = kmem_zalloc(buf_size, KM_SLEEP|KM_NOFS); +@@ -259,6 +259,7 @@ xlog_cil_insert_format_items( + + /* The allocated data region lies beyond the iovec region */ + lv->lv_buf_len = 0; ++ lv->lv_bytes = 0; + lv->lv_buf = (char *)lv + buf_size - nbytes; + ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t))); + -- 2.44.0