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* [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue
@ 2019-10-29  3:13 Ronnie Sahlberg
  2019-10-29  3:13 ` [PATCH] " Ronnie Sahlberg
  0 siblings, 1 reply; 9+ messages in thread
From: Ronnie Sahlberg @ 2019-10-29  3:13 UTC (permalink / raw)
  To: linux-cifs

Pavel,

Please see version 2 addressing your review comments.



^ permalink raw reply	[flat|nested] 9+ messages in thread

* [PATCH] cifs: move cifsFileInfo_put logic into a work-queue
  2019-10-29  3:13 [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue Ronnie Sahlberg
@ 2019-10-29  3:13 ` " Ronnie Sahlberg
  2019-10-29 23:19   ` Pavel Shilovsky
  0 siblings, 1 reply; 9+ messages in thread
From: Ronnie Sahlberg @ 2019-10-29  3:13 UTC (permalink / raw)
  To: linux-cifs; +Cc: Ronnie Sahlberg

This patch moves the final part of the cifsFileInfo_put() logic where we
need a write lock on lock_sem to be processed in a separate thread that
holds no other locks.
This is to prevent deadlocks like the one below:

> there are 6 processes looping to while trying to down_write
> cinode->lock_sem, 5 of them from _cifsFileInfo_put, and one from
> cifs_new_fileinfo
>
> and there are 5 other processes which are blocked, several of them
> waiting on either PG_writeback or PG_locked (which are both set), all
> for the same page of the file
>
> 2 inode_lock() (inode->i_rwsem) for the file
> 1 wait_on_page_writeback() for the page
> 1 down_read(inode->i_rwsem) for the inode of the directory
> 1 inode_lock()(inode->i_rwsem) for the inode of the directory
> 1 __lock_page
>
>
> so processes are blocked waiting on:
>   page flags PG_locked and PG_writeback for one specific page
>   inode->i_rwsem for the directory
>   inode->i_rwsem for the file
>   cifsInodeInflock_sem
>
>
>
> here are the more gory details (let me know if I need to provide
> anything more/better):
>
> [0 00:48:22.765] [UN]  PID: 8863   TASK: ffff8c691547c5c0  CPU: 3
> COMMAND: "reopen_file"
>  #0 [ffff9965007e3ba8] __schedule at ffffffff9b6e6095
>  #1 [ffff9965007e3c38] schedule at ffffffff9b6e64df
>  #2 [ffff9965007e3c48] rwsem_down_write_slowpath at ffffffff9af283d7
>  #3 [ffff9965007e3cb8] legitimize_path at ffffffff9b0f975d
>  #4 [ffff9965007e3d08] path_openat at ffffffff9b0fe55d
>  #5 [ffff9965007e3dd8] do_filp_open at ffffffff9b100a33
>  #6 [ffff9965007e3ee0] do_sys_open at ffffffff9b0eb2d6
>  #7 [ffff9965007e3f38] do_syscall_64 at ffffffff9ae04315
> * (I think legitimize_path is bogus)
>
> in path_openat
>         } else {
>                 const char *s = path_init(nd, flags);
>                 while (!(error = link_path_walk(s, nd)) &&
>                         (error = do_last(nd, file, op)) > 0) {  <<<<
>
> do_last:
>         if (open_flag & O_CREAT)
>                 inode_lock(dir->d_inode);  <<<<
>         else
> so it's trying to take inode->i_rwsem for the directory
>
>      DENTRY           INODE           SUPERBLK     TYPE PATH
> ffff8c68bb8e79c0 ffff8c691158ef20 ffff8c6915bf9000 DIR  /mnt/vm1_smb/
> inode.i_rwsem is ffff8c691158efc0
>
> <struct rw_semaphore 0xffff8c691158efc0>:
>         owner: <struct task_struct 0xffff8c6914275d00> (UN -   8856 -
> reopen_file), counter: 0x0000000000000003
>         waitlist: 2
>         0xffff9965007e3c90     8863   reopen_file      UN 0  1:29:22.926
>   RWSEM_WAITING_FOR_WRITE
>         0xffff996500393e00     9802   ls               UN 0  1:17:26.700
>   RWSEM_WAITING_FOR_READ
>
>
> the owner of the inode.i_rwsem of the directory is:
>
> [0 00:00:00.109] [UN]  PID: 8856   TASK: ffff8c6914275d00  CPU: 3
> COMMAND: "reopen_file"
>  #0 [ffff99650065b828] __schedule at ffffffff9b6e6095
>  #1 [ffff99650065b8b8] schedule at ffffffff9b6e64df
>  #2 [ffff99650065b8c8] schedule_timeout at ffffffff9b6e9f89
>  #3 [ffff99650065b940] msleep at ffffffff9af573a9
>  #4 [ffff99650065b948] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
>  #5 [ffff99650065ba38] cifs_writepage_locked at ffffffffc0a0b8f3 [cifs]
>  #6 [ffff99650065bab0] cifs_launder_page at ffffffffc0a0bb72 [cifs]
>  #7 [ffff99650065bb30] invalidate_inode_pages2_range at ffffffff9b04d4bd
>  #8 [ffff99650065bcb8] cifs_invalidate_mapping at ffffffffc0a11339 [cifs]
>  #9 [ffff99650065bcd0] cifs_revalidate_mapping at ffffffffc0a1139a [cifs]
> #10 [ffff99650065bcf0] cifs_d_revalidate at ffffffffc0a014f6 [cifs]
> #11 [ffff99650065bd08] path_openat at ffffffff9b0fe7f7
> #12 [ffff99650065bdd8] do_filp_open at ffffffff9b100a33
> #13 [ffff99650065bee0] do_sys_open at ffffffff9b0eb2d6
> #14 [ffff99650065bf38] do_syscall_64 at ffffffff9ae04315
>
> cifs_launder_page is for page 0xffffd1e2c07d2480
>
> crash> page.index,mapping,flags 0xffffd1e2c07d2480
>       index = 0x8
>       mapping = 0xffff8c68f3cd0db0
>   flags = 0xfffffc0008095
>
>   PAGE-FLAG       BIT  VALUE
>   PG_locked         0  0000001
>   PG_uptodate       2  0000004
>   PG_lru            4  0000010
>   PG_waiters        7  0000080
>   PG_writeback     15  0008000
>
>
> inode is ffff8c68f3cd0c40
> inode.i_rwsem is ffff8c68f3cd0ce0
>      DENTRY           INODE           SUPERBLK     TYPE PATH
> ffff8c68a1f1b480 ffff8c68f3cd0c40 ffff8c6915bf9000 REG
> /mnt/vm1_smb/testfile.8853
>
>
> this process holds the inode->i_rwsem for the parent directory, is
> laundering a page attached to the inode of the file it's opening, and in
> _cifsFileInfo_put is trying to down_write the cifsInodeInflock_sem
> for the file itself.
>
>
> <struct rw_semaphore 0xffff8c68f3cd0ce0>:
>         owner: <struct task_struct 0xffff8c6914272e80> (UN -   8854 -
> reopen_file), counter: 0x0000000000000003
>         waitlist: 1
>         0xffff9965005dfd80     8855   reopen_file      UN 0  1:29:22.912
>   RWSEM_WAITING_FOR_WRITE
>
> this is the inode.i_rwsem for the file
>
> the owner:
>
> [0 00:48:22.739] [UN]  PID: 8854   TASK: ffff8c6914272e80  CPU: 2
> COMMAND: "reopen_file"
>  #0 [ffff99650054fb38] __schedule at ffffffff9b6e6095
>  #1 [ffff99650054fbc8] schedule at ffffffff9b6e64df
>  #2 [ffff99650054fbd8] io_schedule at ffffffff9b6e68e2
>  #3 [ffff99650054fbe8] __lock_page at ffffffff9b03c56f
>  #4 [ffff99650054fc80] pagecache_get_page at ffffffff9b03dcdf
>  #5 [ffff99650054fcc0] grab_cache_page_write_begin at ffffffff9b03ef4c
>  #6 [ffff99650054fcd0] cifs_write_begin at ffffffffc0a064ec [cifs]
>  #7 [ffff99650054fd30] generic_perform_write at ffffffff9b03bba4
>  #8 [ffff99650054fda8] __generic_file_write_iter at ffffffff9b04060a
>  #9 [ffff99650054fdf0] cifs_strict_writev.cold.70 at ffffffffc0a4469b [cifs]
> #10 [ffff99650054fe48] new_sync_write at ffffffff9b0ec1dd
> #11 [ffff99650054fed0] vfs_write at ffffffff9b0eed35
> #12 [ffff99650054ff00] ksys_write at ffffffff9b0eefd9
> #13 [ffff99650054ff38] do_syscall_64 at ffffffff9ae04315
>
> the process holds the inode->i_rwsem for the file to which it's writing,
> and is trying to __lock_page for the same page as in the other processes
>
>
> the other tasks:
> [0 00:00:00.028] [UN]  PID: 8859   TASK: ffff8c6915479740  CPU: 2
> COMMAND: "reopen_file"
>  #0 [ffff9965007b39d8] __schedule at ffffffff9b6e6095
>  #1 [ffff9965007b3a68] schedule at ffffffff9b6e64df
>  #2 [ffff9965007b3a78] schedule_timeout at ffffffff9b6e9f89
>  #3 [ffff9965007b3af0] msleep at ffffffff9af573a9
>  #4 [ffff9965007b3af8] cifs_new_fileinfo.cold.61 at ffffffffc0a42a07 [cifs]
>  #5 [ffff9965007b3b78] cifs_open at ffffffffc0a0709d [cifs]
>  #6 [ffff9965007b3cd8] do_dentry_open at ffffffff9b0e9b7a
>  #7 [ffff9965007b3d08] path_openat at ffffffff9b0fe34f
>  #8 [ffff9965007b3dd8] do_filp_open at ffffffff9b100a33
>  #9 [ffff9965007b3ee0] do_sys_open at ffffffff9b0eb2d6
> #10 [ffff9965007b3f38] do_syscall_64 at ffffffff9ae04315
>
> this is opening the file, and is trying to down_write cinode->lock_sem
>
>
> [0 00:00:00.041] [UN]  PID: 8860   TASK: ffff8c691547ae80  CPU: 2
> COMMAND: "reopen_file"
> [0 00:00:00.057] [UN]  PID: 8861   TASK: ffff8c6915478000  CPU: 3
> COMMAND: "reopen_file"
> [0 00:00:00.059] [UN]  PID: 8858   TASK: ffff8c6914271740  CPU: 2
> COMMAND: "reopen_file"
> [0 00:00:00.109] [UN]  PID: 8862   TASK: ffff8c691547dd00  CPU: 6
> COMMAND: "reopen_file"
>  #0 [ffff9965007c3c78] __schedule at ffffffff9b6e6095
>  #1 [ffff9965007c3d08] schedule at ffffffff9b6e64df
>  #2 [ffff9965007c3d18] schedule_timeout at ffffffff9b6e9f89
>  #3 [ffff9965007c3d90] msleep at ffffffff9af573a9
>  #4 [ffff9965007c3d98] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
>  #5 [ffff9965007c3e88] cifs_close at ffffffffc0a07aaf [cifs]
>  #6 [ffff9965007c3ea0] __fput at ffffffff9b0efa6e
>  #7 [ffff9965007c3ee8] task_work_run at ffffffff9aef1614
>  #8 [ffff9965007c3f20] exit_to_usermode_loop at ffffffff9ae03d6f
>  #9 [ffff9965007c3f38] do_syscall_64 at ffffffff9ae0444c
>
> closing the file, and trying to down_write cifsi->lock_sem
>
>
> [0 00:48:22.839] [UN]  PID: 8857   TASK: ffff8c6914270000  CPU: 7
> COMMAND: "reopen_file"
>  #0 [ffff9965006a7cc8] __schedule at ffffffff9b6e6095
>  #1 [ffff9965006a7d58] schedule at ffffffff9b6e64df
>  #2 [ffff9965006a7d68] io_schedule at ffffffff9b6e68e2
>  #3 [ffff9965006a7d78] wait_on_page_bit at ffffffff9b03cac6
>  #4 [ffff9965006a7e10] __filemap_fdatawait_range at ffffffff9b03b028
>  #5 [ffff9965006a7ed8] filemap_write_and_wait at ffffffff9b040165
>  #6 [ffff9965006a7ef0] cifs_flush at ffffffffc0a0c2fa [cifs]
>  #7 [ffff9965006a7f10] filp_close at ffffffff9b0e93f1
>  #8 [ffff9965006a7f30] __x64_sys_close at ffffffff9b0e9a0e
>  #9 [ffff9965006a7f38] do_syscall_64 at ffffffff9ae04315
>
> in __filemap_fdatawait_range
>                         wait_on_page_writeback(page);
> for the same page of the file
>
>
>
> [0 00:48:22.718] [UN]  PID: 8855   TASK: ffff8c69142745c0  CPU: 7
> COMMAND: "reopen_file"
>  #0 [ffff9965005dfc98] __schedule at ffffffff9b6e6095
>  #1 [ffff9965005dfd28] schedule at ffffffff9b6e64df
>  #2 [ffff9965005dfd38] rwsem_down_write_slowpath at ffffffff9af283d7
>  #3 [ffff9965005dfdf0] cifs_strict_writev at ffffffffc0a0c40a [cifs]
>  #4 [ffff9965005dfe48] new_sync_write at ffffffff9b0ec1dd
>  #5 [ffff9965005dfed0] vfs_write at ffffffff9b0eed35
>  #6 [ffff9965005dff00] ksys_write at ffffffff9b0eefd9
>  #7 [ffff9965005dff38] do_syscall_64 at ffffffff9ae04315
>
>         inode_lock(inode);
>
>
> and one 'ls' later on, to see whether the rest of the mount is available
> (the test file is in the root, so we get blocked up on the directory
> ->i_rwsem), so the entire mount is unavailable
>
> [0 00:36:26.473] [UN]  PID: 9802   TASK: ffff8c691436ae80  CPU: 4
> COMMAND: "ls"
>  #0 [ffff996500393d28] __schedule at ffffffff9b6e6095
>  #1 [ffff996500393db8] schedule at ffffffff9b6e64df
>  #2 [ffff996500393dc8] rwsem_down_read_slowpath at ffffffff9b6e9421
>  #3 [ffff996500393e78] down_read_killable at ffffffff9b6e95e2
>  #4 [ffff996500393e88] iterate_dir at ffffffff9b103c56
>  #5 [ffff996500393ec8] ksys_getdents64 at ffffffff9b104b0c
>  #6 [ffff996500393f30] __x64_sys_getdents64 at ffffffff9b104bb6
>  #7 [ffff996500393f38] do_syscall_64 at ffffffff9ae04315
>
> in iterate_dir:
>         if (shared)
>                 res = down_read_killable(&inode->i_rwsem);  <<<<
>         else
>                 res = down_write_killable(&inode->i_rwsem);
>

Reported-by: Frank Sorenson <sorenson@redhat.com>:
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/cifsfs.c   | 13 +++++++++-
 fs/cifs/cifsglob.h |  5 +++-
 fs/cifs/file.c     | 72 +++++++++++++++++++++++++++++++++++-------------------
 3 files changed, 63 insertions(+), 27 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index e4e3b573d20c..f8e201c45ccb 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -119,6 +119,7 @@ extern mempool_t *cifs_mid_poolp;
 
 struct workqueue_struct	*cifsiod_wq;
 struct workqueue_struct	*decrypt_wq;
+struct workqueue_struct	*fileinfo_put_wq;
 struct workqueue_struct	*cifsoplockd_wq;
 __u32 cifs_lock_secret;
 
@@ -1557,11 +1558,18 @@ init_cifs(void)
 		goto out_destroy_cifsiod_wq;
 	}
 
+	fileinfo_put_wq = alloc_workqueue("cifsfileinfoput",
+				     WQ_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
+	if (!fileinfo_put_wq) {
+		rc = -ENOMEM;
+		goto out_destroy_decrypt_wq;
+	}
+
 	cifsoplockd_wq = alloc_workqueue("cifsoplockd",
 					 WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
 	if (!cifsoplockd_wq) {
 		rc = -ENOMEM;
-		goto out_destroy_decrypt_wq;
+		goto out_destroy_fileinfo_put_wq;
 	}
 
 	rc = cifs_fscache_register();
@@ -1627,6 +1635,8 @@ init_cifs(void)
 	cifs_fscache_unregister();
 out_destroy_cifsoplockd_wq:
 	destroy_workqueue(cifsoplockd_wq);
+out_destroy_fileinfo_put_wq:
+	destroy_workqueue(fileinfo_put_wq);
 out_destroy_decrypt_wq:
 	destroy_workqueue(decrypt_wq);
 out_destroy_cifsiod_wq:
@@ -1656,6 +1666,7 @@ exit_cifs(void)
 	cifs_fscache_unregister();
 	destroy_workqueue(cifsoplockd_wq);
 	destroy_workqueue(decrypt_wq);
+	destroy_workqueue(fileinfo_put_wq);
 	destroy_workqueue(cifsiod_wq);
 	cifs_proc_clean();
 }
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index d78bfcc19156..e0a7dc3f62b2 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -1265,6 +1265,7 @@ struct cifsFileInfo {
 	struct mutex fh_mutex; /* prevents reopen race after dead ses*/
 	struct cifs_search_info srch_inf;
 	struct work_struct oplock_break; /* work for oplock breaks */
+	struct work_struct put; /* work for the final part of _put */
 };
 
 struct cifs_io_parms {
@@ -1370,7 +1371,8 @@ cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
 }
 
 struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
-void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr);
+void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr,
+		       bool offload);
 void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
 
 #define CIFS_CACHE_READ_FLG	1
@@ -1907,6 +1909,7 @@ void cifs_queue_oplock_break(struct cifsFileInfo *cfile);
 extern const struct slow_work_ops cifs_oplock_break_ops;
 extern struct workqueue_struct *cifsiod_wq;
 extern struct workqueue_struct *decrypt_wq;
+extern struct workqueue_struct *fileinfo_put_wq;
 extern struct workqueue_struct *cifsoplockd_wq;
 extern __u32 cifs_lock_secret;
 
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 67e7d0ffe385..309d6948d2f4 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -375,6 +375,41 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
 	return cifs_file;
 }
 
+static void cifsFileInfo_put_final(struct cifsFileInfo *cifs_file)
+{
+	struct inode *inode = d_inode(cifs_file->dentry);
+	struct cifsInodeInfo *cifsi = CIFS_I(inode);
+	struct cifsLockInfo *li, *tmp;
+	struct super_block *sb = inode->i_sb;
+
+	/*
+	 * Delete any outstanding lock records. We'll lose them when the file
+	 * is closed anyway.
+	 */
+	cifs_down_write(&cifsi->lock_sem);
+	list_for_each_entry_safe(li, tmp, &cifs_file->llist->locks, llist) {
+		list_del(&li->llist);
+		cifs_del_lock_waiters(li);
+		kfree(li);
+	}
+	list_del(&cifs_file->llist->llist);
+	kfree(cifs_file->llist);
+	up_write(&cifsi->lock_sem);
+
+	cifs_put_tlink(cifs_file->tlink);
+	dput(cifs_file->dentry);
+	cifs_sb_deactive(sb);
+	kfree(cifs_file);
+}
+
+static void cifsFileInfo_put_work(struct work_struct *work)
+{
+	struct cifsFileInfo *cifs_file = container_of(work,
+			struct cifsFileInfo, put);
+
+	cifsFileInfo_put_final(cifs_file);
+}
+
 /**
  * cifsFileInfo_put - release a reference of file priv data
  *
@@ -382,15 +417,15 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
  */
 void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
 {
-	_cifsFileInfo_put(cifs_file, true);
+  _cifsFileInfo_put(cifs_file, true, true);
 }
 
 /**
  * _cifsFileInfo_put - release a reference of file priv data
  *
  * This may involve closing the filehandle @cifs_file out on the
- * server. Must be called without holding tcon->open_file_lock and
- * cifs_file->file_info_lock.
+ * server. Must be called without holding tcon->open_file_lock,
+ * cinode->open_file_lock and cifs_file->file_info_lock.
  *
  * If @wait_for_oplock_handler is true and we are releasing the last
  * reference, wait for any running oplock break handler of the file
@@ -398,7 +433,8 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
  * oplock break handler, you need to pass false.
  *
  */
-void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
+void _cifsFileInfo_put(struct cifsFileInfo *cifs_file,
+		       bool wait_oplock_handler, bool offload)
 {
 	struct inode *inode = d_inode(cifs_file->dentry);
 	struct cifs_tcon *tcon = tlink_tcon(cifs_file->tlink);
@@ -406,7 +442,6 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
 	struct cifsInodeInfo *cifsi = CIFS_I(inode);
 	struct super_block *sb = inode->i_sb;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(sb);
-	struct cifsLockInfo *li, *tmp;
 	struct cifs_fid fid;
 	struct cifs_pending_open open;
 	bool oplock_break_cancelled;
@@ -467,24 +502,11 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
 
 	cifs_del_pending_open(&open);
 
-	/*
-	 * Delete any outstanding lock records. We'll lose them when the file
-	 * is closed anyway.
-	 */
-	cifs_down_write(&cifsi->lock_sem);
-	list_for_each_entry_safe(li, tmp, &cifs_file->llist->locks, llist) {
-		list_del(&li->llist);
-		cifs_del_lock_waiters(li);
-		kfree(li);
-	}
-	list_del(&cifs_file->llist->llist);
-	kfree(cifs_file->llist);
-	up_write(&cifsi->lock_sem);
-
-	cifs_put_tlink(cifs_file->tlink);
-	dput(cifs_file->dentry);
-	cifs_sb_deactive(sb);
-	kfree(cifs_file);
+	if (offload) {
+		INIT_WORK(&cifs_file->put, cifsFileInfo_put_work);
+		queue_work(fileinfo_put_wq, &cifs_file->put);
+	} else
+		cifsFileInfo_put_final(cifs_file);
 }
 
 int cifs_open(struct inode *inode, struct file *file)
@@ -808,7 +830,7 @@ cifs_reopen_file(struct cifsFileInfo *cfile, bool can_flush)
 int cifs_close(struct inode *inode, struct file *file)
 {
 	if (file->private_data != NULL) {
-		cifsFileInfo_put(file->private_data);
+		_cifsFileInfo_put(file->private_data, true, false);
 		file->private_data = NULL;
 	}
 
@@ -4742,7 +4764,7 @@ void cifs_oplock_break(struct work_struct *work)
 							     cinode);
 		cifs_dbg(FYI, "Oplock release rc = %d\n", rc);
 	}
-	_cifsFileInfo_put(cfile, false /* do not wait for ourself */);
+	_cifsFileInfo_put(cfile, false /* do not wait for ourself */, false);
 	cifs_done_oplock_break(cinode);
 }
 
-- 
2.13.6


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH] cifs: move cifsFileInfo_put logic into a work-queue
  2019-10-29  3:13 ` [PATCH] " Ronnie Sahlberg
@ 2019-10-29 23:19   ` Pavel Shilovsky
  2019-10-30  1:25     ` ronnie sahlberg
  0 siblings, 1 reply; 9+ messages in thread
From: Pavel Shilovsky @ 2019-10-29 23:19 UTC (permalink / raw)
  To: Ronnie Sahlberg; +Cc: linux-cifs

вт, 29 окт. 2019 г. в 00:25, Ronnie Sahlberg <lsahlber@redhat.com>:
>
> This patch moves the final part of the cifsFileInfo_put() logic where we
> need a write lock on lock_sem to be processed in a separate thread that
> holds no other locks.
> This is to prevent deadlocks like the one below:
>
> > there are 6 processes looping to while trying to down_write
> > cinode->lock_sem, 5 of them from _cifsFileInfo_put, and one from
> > cifs_new_fileinfo
> >
> > and there are 5 other processes which are blocked, several of them
> > waiting on either PG_writeback or PG_locked (which are both set), all
> > for the same page of the file
> >
> > 2 inode_lock() (inode->i_rwsem) for the file
> > 1 wait_on_page_writeback() for the page
> > 1 down_read(inode->i_rwsem) for the inode of the directory
> > 1 inode_lock()(inode->i_rwsem) for the inode of the directory
> > 1 __lock_page
> >
> >
> > so processes are blocked waiting on:
> >   page flags PG_locked and PG_writeback for one specific page
> >   inode->i_rwsem for the directory
> >   inode->i_rwsem for the file
> >   cifsInodeInflock_sem
> >
> >
> >
> > here are the more gory details (let me know if I need to provide
> > anything more/better):
> >
> > [0 00:48:22.765] [UN]  PID: 8863   TASK: ffff8c691547c5c0  CPU: 3
> > COMMAND: "reopen_file"
> >  #0 [ffff9965007e3ba8] __schedule at ffffffff9b6e6095
> >  #1 [ffff9965007e3c38] schedule at ffffffff9b6e64df
> >  #2 [ffff9965007e3c48] rwsem_down_write_slowpath at ffffffff9af283d7
> >  #3 [ffff9965007e3cb8] legitimize_path at ffffffff9b0f975d
> >  #4 [ffff9965007e3d08] path_openat at ffffffff9b0fe55d
> >  #5 [ffff9965007e3dd8] do_filp_open at ffffffff9b100a33
> >  #6 [ffff9965007e3ee0] do_sys_open at ffffffff9b0eb2d6
> >  #7 [ffff9965007e3f38] do_syscall_64 at ffffffff9ae04315
> > * (I think legitimize_path is bogus)
> >
> > in path_openat
> >         } else {
> >                 const char *s = path_init(nd, flags);
> >                 while (!(error = link_path_walk(s, nd)) &&
> >                         (error = do_last(nd, file, op)) > 0) {  <<<<
> >
> > do_last:
> >         if (open_flag & O_CREAT)
> >                 inode_lock(dir->d_inode);  <<<<
> >         else
> > so it's trying to take inode->i_rwsem for the directory
> >
> >      DENTRY           INODE           SUPERBLK     TYPE PATH
> > ffff8c68bb8e79c0 ffff8c691158ef20 ffff8c6915bf9000 DIR  /mnt/vm1_smb/
> > inode.i_rwsem is ffff8c691158efc0
> >
> > <struct rw_semaphore 0xffff8c691158efc0>:
> >         owner: <struct task_struct 0xffff8c6914275d00> (UN -   8856 -
> > reopen_file), counter: 0x0000000000000003
> >         waitlist: 2
> >         0xffff9965007e3c90     8863   reopen_file      UN 0  1:29:22.926
> >   RWSEM_WAITING_FOR_WRITE
> >         0xffff996500393e00     9802   ls               UN 0  1:17:26.700
> >   RWSEM_WAITING_FOR_READ
> >
> >
> > the owner of the inode.i_rwsem of the directory is:
> >
> > [0 00:00:00.109] [UN]  PID: 8856   TASK: ffff8c6914275d00  CPU: 3
> > COMMAND: "reopen_file"
> >  #0 [ffff99650065b828] __schedule at ffffffff9b6e6095
> >  #1 [ffff99650065b8b8] schedule at ffffffff9b6e64df
> >  #2 [ffff99650065b8c8] schedule_timeout at ffffffff9b6e9f89
> >  #3 [ffff99650065b940] msleep at ffffffff9af573a9
> >  #4 [ffff99650065b948] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> >  #5 [ffff99650065ba38] cifs_writepage_locked at ffffffffc0a0b8f3 [cifs]
> >  #6 [ffff99650065bab0] cifs_launder_page at ffffffffc0a0bb72 [cifs]
> >  #7 [ffff99650065bb30] invalidate_inode_pages2_range at ffffffff9b04d4bd
> >  #8 [ffff99650065bcb8] cifs_invalidate_mapping at ffffffffc0a11339 [cifs]
> >  #9 [ffff99650065bcd0] cifs_revalidate_mapping at ffffffffc0a1139a [cifs]
> > #10 [ffff99650065bcf0] cifs_d_revalidate at ffffffffc0a014f6 [cifs]
> > #11 [ffff99650065bd08] path_openat at ffffffff9b0fe7f7
> > #12 [ffff99650065bdd8] do_filp_open at ffffffff9b100a33
> > #13 [ffff99650065bee0] do_sys_open at ffffffff9b0eb2d6
> > #14 [ffff99650065bf38] do_syscall_64 at ffffffff9ae04315
> >
> > cifs_launder_page is for page 0xffffd1e2c07d2480
> >
> > crash> page.index,mapping,flags 0xffffd1e2c07d2480
> >       index = 0x8
> >       mapping = 0xffff8c68f3cd0db0
> >   flags = 0xfffffc0008095
> >
> >   PAGE-FLAG       BIT  VALUE
> >   PG_locked         0  0000001
> >   PG_uptodate       2  0000004
> >   PG_lru            4  0000010
> >   PG_waiters        7  0000080
> >   PG_writeback     15  0008000
> >
> >
> > inode is ffff8c68f3cd0c40
> > inode.i_rwsem is ffff8c68f3cd0ce0
> >      DENTRY           INODE           SUPERBLK     TYPE PATH
> > ffff8c68a1f1b480 ffff8c68f3cd0c40 ffff8c6915bf9000 REG
> > /mnt/vm1_smb/testfile.8853
> >
> >
> > this process holds the inode->i_rwsem for the parent directory, is
> > laundering a page attached to the inode of the file it's opening, and in
> > _cifsFileInfo_put is trying to down_write the cifsInodeInflock_sem
> > for the file itself.
> >
> >
> > <struct rw_semaphore 0xffff8c68f3cd0ce0>:
> >         owner: <struct task_struct 0xffff8c6914272e80> (UN -   8854 -
> > reopen_file), counter: 0x0000000000000003
> >         waitlist: 1
> >         0xffff9965005dfd80     8855   reopen_file      UN 0  1:29:22.912
> >   RWSEM_WAITING_FOR_WRITE
> >
> > this is the inode.i_rwsem for the file
> >
> > the owner:
> >
> > [0 00:48:22.739] [UN]  PID: 8854   TASK: ffff8c6914272e80  CPU: 2
> > COMMAND: "reopen_file"
> >  #0 [ffff99650054fb38] __schedule at ffffffff9b6e6095
> >  #1 [ffff99650054fbc8] schedule at ffffffff9b6e64df
> >  #2 [ffff99650054fbd8] io_schedule at ffffffff9b6e68e2
> >  #3 [ffff99650054fbe8] __lock_page at ffffffff9b03c56f
> >  #4 [ffff99650054fc80] pagecache_get_page at ffffffff9b03dcdf
> >  #5 [ffff99650054fcc0] grab_cache_page_write_begin at ffffffff9b03ef4c
> >  #6 [ffff99650054fcd0] cifs_write_begin at ffffffffc0a064ec [cifs]
> >  #7 [ffff99650054fd30] generic_perform_write at ffffffff9b03bba4
> >  #8 [ffff99650054fda8] __generic_file_write_iter at ffffffff9b04060a
> >  #9 [ffff99650054fdf0] cifs_strict_writev.cold.70 at ffffffffc0a4469b [cifs]
> > #10 [ffff99650054fe48] new_sync_write at ffffffff9b0ec1dd
> > #11 [ffff99650054fed0] vfs_write at ffffffff9b0eed35
> > #12 [ffff99650054ff00] ksys_write at ffffffff9b0eefd9
> > #13 [ffff99650054ff38] do_syscall_64 at ffffffff9ae04315
> >
> > the process holds the inode->i_rwsem for the file to which it's writing,
> > and is trying to __lock_page for the same page as in the other processes
> >
> >
> > the other tasks:
> > [0 00:00:00.028] [UN]  PID: 8859   TASK: ffff8c6915479740  CPU: 2
> > COMMAND: "reopen_file"
> >  #0 [ffff9965007b39d8] __schedule at ffffffff9b6e6095
> >  #1 [ffff9965007b3a68] schedule at ffffffff9b6e64df
> >  #2 [ffff9965007b3a78] schedule_timeout at ffffffff9b6e9f89
> >  #3 [ffff9965007b3af0] msleep at ffffffff9af573a9
> >  #4 [ffff9965007b3af8] cifs_new_fileinfo.cold.61 at ffffffffc0a42a07 [cifs]
> >  #5 [ffff9965007b3b78] cifs_open at ffffffffc0a0709d [cifs]
> >  #6 [ffff9965007b3cd8] do_dentry_open at ffffffff9b0e9b7a
> >  #7 [ffff9965007b3d08] path_openat at ffffffff9b0fe34f
> >  #8 [ffff9965007b3dd8] do_filp_open at ffffffff9b100a33
> >  #9 [ffff9965007b3ee0] do_sys_open at ffffffff9b0eb2d6
> > #10 [ffff9965007b3f38] do_syscall_64 at ffffffff9ae04315
> >
> > this is opening the file, and is trying to down_write cinode->lock_sem
> >
> >
> > [0 00:00:00.041] [UN]  PID: 8860   TASK: ffff8c691547ae80  CPU: 2
> > COMMAND: "reopen_file"
> > [0 00:00:00.057] [UN]  PID: 8861   TASK: ffff8c6915478000  CPU: 3
> > COMMAND: "reopen_file"
> > [0 00:00:00.059] [UN]  PID: 8858   TASK: ffff8c6914271740  CPU: 2
> > COMMAND: "reopen_file"
> > [0 00:00:00.109] [UN]  PID: 8862   TASK: ffff8c691547dd00  CPU: 6
> > COMMAND: "reopen_file"
> >  #0 [ffff9965007c3c78] __schedule at ffffffff9b6e6095
> >  #1 [ffff9965007c3d08] schedule at ffffffff9b6e64df
> >  #2 [ffff9965007c3d18] schedule_timeout at ffffffff9b6e9f89
> >  #3 [ffff9965007c3d90] msleep at ffffffff9af573a9
> >  #4 [ffff9965007c3d98] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> >  #5 [ffff9965007c3e88] cifs_close at ffffffffc0a07aaf [cifs]
> >  #6 [ffff9965007c3ea0] __fput at ffffffff9b0efa6e
> >  #7 [ffff9965007c3ee8] task_work_run at ffffffff9aef1614
> >  #8 [ffff9965007c3f20] exit_to_usermode_loop at ffffffff9ae03d6f
> >  #9 [ffff9965007c3f38] do_syscall_64 at ffffffff9ae0444c
> >
> > closing the file, and trying to down_write cifsi->lock_sem
> >
> >
> > [0 00:48:22.839] [UN]  PID: 8857   TASK: ffff8c6914270000  CPU: 7
> > COMMAND: "reopen_file"
> >  #0 [ffff9965006a7cc8] __schedule at ffffffff9b6e6095
> >  #1 [ffff9965006a7d58] schedule at ffffffff9b6e64df
> >  #2 [ffff9965006a7d68] io_schedule at ffffffff9b6e68e2
> >  #3 [ffff9965006a7d78] wait_on_page_bit at ffffffff9b03cac6
> >  #4 [ffff9965006a7e10] __filemap_fdatawait_range at ffffffff9b03b028
> >  #5 [ffff9965006a7ed8] filemap_write_and_wait at ffffffff9b040165
> >  #6 [ffff9965006a7ef0] cifs_flush at ffffffffc0a0c2fa [cifs]
> >  #7 [ffff9965006a7f10] filp_close at ffffffff9b0e93f1
> >  #8 [ffff9965006a7f30] __x64_sys_close at ffffffff9b0e9a0e
> >  #9 [ffff9965006a7f38] do_syscall_64 at ffffffff9ae04315
> >
> > in __filemap_fdatawait_range
> >                         wait_on_page_writeback(page);
> > for the same page of the file
> >
> >
> >
> > [0 00:48:22.718] [UN]  PID: 8855   TASK: ffff8c69142745c0  CPU: 7
> > COMMAND: "reopen_file"
> >  #0 [ffff9965005dfc98] __schedule at ffffffff9b6e6095
> >  #1 [ffff9965005dfd28] schedule at ffffffff9b6e64df
> >  #2 [ffff9965005dfd38] rwsem_down_write_slowpath at ffffffff9af283d7
> >  #3 [ffff9965005dfdf0] cifs_strict_writev at ffffffffc0a0c40a [cifs]
> >  #4 [ffff9965005dfe48] new_sync_write at ffffffff9b0ec1dd
> >  #5 [ffff9965005dfed0] vfs_write at ffffffff9b0eed35
> >  #6 [ffff9965005dff00] ksys_write at ffffffff9b0eefd9
> >  #7 [ffff9965005dff38] do_syscall_64 at ffffffff9ae04315
> >
> >         inode_lock(inode);
> >
> >
> > and one 'ls' later on, to see whether the rest of the mount is available
> > (the test file is in the root, so we get blocked up on the directory
> > ->i_rwsem), so the entire mount is unavailable
> >
> > [0 00:36:26.473] [UN]  PID: 9802   TASK: ffff8c691436ae80  CPU: 4
> > COMMAND: "ls"
> >  #0 [ffff996500393d28] __schedule at ffffffff9b6e6095
> >  #1 [ffff996500393db8] schedule at ffffffff9b6e64df
> >  #2 [ffff996500393dc8] rwsem_down_read_slowpath at ffffffff9b6e9421
> >  #3 [ffff996500393e78] down_read_killable at ffffffff9b6e95e2
> >  #4 [ffff996500393e88] iterate_dir at ffffffff9b103c56
> >  #5 [ffff996500393ec8] ksys_getdents64 at ffffffff9b104b0c
> >  #6 [ffff996500393f30] __x64_sys_getdents64 at ffffffff9b104bb6
> >  #7 [ffff996500393f38] do_syscall_64 at ffffffff9ae04315
> >
> > in iterate_dir:
> >         if (shared)
> >                 res = down_read_killable(&inode->i_rwsem);  <<<<
> >         else
> >                 res = down_write_killable(&inode->i_rwsem);
> >

Thanks for the update.

I would suggest to shorten the description to include only two traces
of deadlocked processes to improve readability. Please find my other
comments below.

>
> Reported-by: Frank Sorenson <sorenson@redhat.com>:
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>  fs/cifs/cifsfs.c   | 13 +++++++++-
>  fs/cifs/cifsglob.h |  5 +++-
>  fs/cifs/file.c     | 72 +++++++++++++++++++++++++++++++++++-------------------
>  3 files changed, 63 insertions(+), 27 deletions(-)
>
> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> index e4e3b573d20c..f8e201c45ccb 100644
> --- a/fs/cifs/cifsfs.c
> +++ b/fs/cifs/cifsfs.c
> @@ -119,6 +119,7 @@ extern mempool_t *cifs_mid_poolp;
>
>  struct workqueue_struct        *cifsiod_wq;
>  struct workqueue_struct        *decrypt_wq;
> +struct workqueue_struct        *fileinfo_put_wq;
>  struct workqueue_struct        *cifsoplockd_wq;
>  __u32 cifs_lock_secret;
>
> @@ -1557,11 +1558,18 @@ init_cifs(void)
>                 goto out_destroy_cifsiod_wq;
>         }
>
> +       fileinfo_put_wq = alloc_workqueue("cifsfileinfoput",
> +                                    WQ_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> +       if (!fileinfo_put_wq) {
> +               rc = -ENOMEM;
> +               goto out_destroy_decrypt_wq;
> +       }
> +
>         cifsoplockd_wq = alloc_workqueue("cifsoplockd",
>                                          WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
>         if (!cifsoplockd_wq) {
>                 rc = -ENOMEM;
> -               goto out_destroy_decrypt_wq;
> +               goto out_destroy_fileinfo_put_wq;
>         }
>
>         rc = cifs_fscache_register();
> @@ -1627,6 +1635,8 @@ init_cifs(void)
>         cifs_fscache_unregister();
>  out_destroy_cifsoplockd_wq:
>         destroy_workqueue(cifsoplockd_wq);
> +out_destroy_fileinfo_put_wq:
> +       destroy_workqueue(fileinfo_put_wq);
>  out_destroy_decrypt_wq:
>         destroy_workqueue(decrypt_wq);
>  out_destroy_cifsiod_wq:
> @@ -1656,6 +1666,7 @@ exit_cifs(void)
>         cifs_fscache_unregister();
>         destroy_workqueue(cifsoplockd_wq);
>         destroy_workqueue(decrypt_wq);
> +       destroy_workqueue(fileinfo_put_wq);
>         destroy_workqueue(cifsiod_wq);
>         cifs_proc_clean();
>  }
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index d78bfcc19156..e0a7dc3f62b2 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -1265,6 +1265,7 @@ struct cifsFileInfo {
>         struct mutex fh_mutex; /* prevents reopen race after dead ses*/
>         struct cifs_search_info srch_inf;
>         struct work_struct oplock_break; /* work for oplock breaks */
> +       struct work_struct put; /* work for the final part of _put */
>  };
>
>  struct cifs_io_parms {
> @@ -1370,7 +1371,8 @@ cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
>  }
>
>  struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
> -void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr);
> +void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr,
> +                      bool offload);

Do we still need wait_oplock_hdlr here? It is only being used in
cifs_oplock_break() and it seems that we can easily remove it and just
offload that occurrence to the worker thread archiving the same
functionality.

>  void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
>
>  #define CIFS_CACHE_READ_FLG    1
> @@ -1907,6 +1909,7 @@ void cifs_queue_oplock_break(struct cifsFileInfo *cfile);
>  extern const struct slow_work_ops cifs_oplock_break_ops;
>  extern struct workqueue_struct *cifsiod_wq;
>  extern struct workqueue_struct *decrypt_wq;
> +extern struct workqueue_struct *fileinfo_put_wq;
>  extern struct workqueue_struct *cifsoplockd_wq;
>  extern __u32 cifs_lock_secret;
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 67e7d0ffe385..309d6948d2f4 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -375,6 +375,41 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
>         return cifs_file;
>  }
>
> +static void cifsFileInfo_put_final(struct cifsFileInfo *cifs_file)

This should work but I actually meant something different: to offload
the whole _cifsFileInfo_put() by renaming it to
cifsFileInfo_put_final() as is and adding new _cifsFileInfo_put() -
see below.

_cifsFileInfo_put(cifs_file, wait_oplock_handler, offload)
{

[ with optimizations ]
// acquire only file info lock
// check reference
// if ref=1 and offload=True then put the work in the queue, drop the
file info lock and exit
// else if ref>1 then just decrement, drop the lock and exit - no need
to take tcon and inode locks because we don't modify those lists
// else (meaning ref=1 and offload=False) drop the file info lock and
call cifsFileInfo_put_final()

OR

[ without optimizations ]
// just use qeueue_work() all the time when offload=True

}

The reason why I think it's better is that we can make further use of
it for BATCH oplocks implementation. In case of closing a file with
BATCH oplock, we may change a function above to call mod_queue_work()
with some timeout instead of queue_work(). Then another open call
comes, looks up the cifsFileInfo structure in the open file list and
increments the reference. By the time when the mod_queue_work timeout
expires and the worker thread decrements the reference it will remain
positive thus available for the existing and other open calls to use:

Example of possible execution:

0s T1 opens a file and gets BATCH oplock - reference is 1;
1s T1 closes the file by calling cifsFileInfo_put(cfile, true, true)
and put cifsFileInfo in the work queue with 10s timeout;
2s T1 opens the same file, looks it up in the open file list and
increment the reference to 2;
...
11s T2 pulls cifsFileInfo from the work queue, calls and decrement the
reference to 1;
12s T2 closes the file and put cifsFileInfo in the work queue with 10s timeout;
...
22s T3 pulls cifsFileInfo from the work queue, decrements the
reference to 0 and does all the cleanup steps from
cifsFileInfo_put_final().

This should significantly improve performance of applications that do
many open-close calls on the same file and it won't require a lot of
code changes.

The above suggestions (to offload the whole _cifsFileInfo_put) doesn't
seem like a big change to your current patch but it also may be done
as a followup patch, so, leaving it up to you What do you think?

--
Best regards,
Pavel Shilovsky

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH] cifs: move cifsFileInfo_put logic into a work-queue
  2019-10-29 23:19   ` Pavel Shilovsky
@ 2019-10-30  1:25     ` ronnie sahlberg
  2019-10-30 15:57       ` Pavel Shilovsky
  0 siblings, 1 reply; 9+ messages in thread
From: ronnie sahlberg @ 2019-10-30  1:25 UTC (permalink / raw)
  To: Pavel Shilovsky; +Cc: Ronnie Sahlberg, linux-cifs

On Wed, Oct 30, 2019 at 9:22 AM Pavel Shilovsky <piastryyy@gmail.com> wrote:
>
> вт, 29 окт. 2019 г. в 00:25, Ronnie Sahlberg <lsahlber@redhat.com>:
> >
> > This patch moves the final part of the cifsFileInfo_put() logic where we
> > need a write lock on lock_sem to be processed in a separate thread that
> > holds no other locks.
> > This is to prevent deadlocks like the one below:
> >
> > > there are 6 processes looping to while trying to down_write
> > > cinode->lock_sem, 5 of them from _cifsFileInfo_put, and one from
> > > cifs_new_fileinfo
> > >
> > > and there are 5 other processes which are blocked, several of them
> > > waiting on either PG_writeback or PG_locked (which are both set), all
> > > for the same page of the file
> > >
> > > 2 inode_lock() (inode->i_rwsem) for the file
> > > 1 wait_on_page_writeback() for the page
> > > 1 down_read(inode->i_rwsem) for the inode of the directory
> > > 1 inode_lock()(inode->i_rwsem) for the inode of the directory
> > > 1 __lock_page
> > >
> > >
> > > so processes are blocked waiting on:
> > >   page flags PG_locked and PG_writeback for one specific page
> > >   inode->i_rwsem for the directory
> > >   inode->i_rwsem for the file
> > >   cifsInodeInflock_sem
> > >
> > >
> > >
> > > here are the more gory details (let me know if I need to provide
> > > anything more/better):
> > >
> > > [0 00:48:22.765] [UN]  PID: 8863   TASK: ffff8c691547c5c0  CPU: 3
> > > COMMAND: "reopen_file"
> > >  #0 [ffff9965007e3ba8] __schedule at ffffffff9b6e6095
> > >  #1 [ffff9965007e3c38] schedule at ffffffff9b6e64df
> > >  #2 [ffff9965007e3c48] rwsem_down_write_slowpath at ffffffff9af283d7
> > >  #3 [ffff9965007e3cb8] legitimize_path at ffffffff9b0f975d
> > >  #4 [ffff9965007e3d08] path_openat at ffffffff9b0fe55d
> > >  #5 [ffff9965007e3dd8] do_filp_open at ffffffff9b100a33
> > >  #6 [ffff9965007e3ee0] do_sys_open at ffffffff9b0eb2d6
> > >  #7 [ffff9965007e3f38] do_syscall_64 at ffffffff9ae04315
> > > * (I think legitimize_path is bogus)
> > >
> > > in path_openat
> > >         } else {
> > >                 const char *s = path_init(nd, flags);
> > >                 while (!(error = link_path_walk(s, nd)) &&
> > >                         (error = do_last(nd, file, op)) > 0) {  <<<<
> > >
> > > do_last:
> > >         if (open_flag & O_CREAT)
> > >                 inode_lock(dir->d_inode);  <<<<
> > >         else
> > > so it's trying to take inode->i_rwsem for the directory
> > >
> > >      DENTRY           INODE           SUPERBLK     TYPE PATH
> > > ffff8c68bb8e79c0 ffff8c691158ef20 ffff8c6915bf9000 DIR  /mnt/vm1_smb/
> > > inode.i_rwsem is ffff8c691158efc0
> > >
> > > <struct rw_semaphore 0xffff8c691158efc0>:
> > >         owner: <struct task_struct 0xffff8c6914275d00> (UN -   8856 -
> > > reopen_file), counter: 0x0000000000000003
> > >         waitlist: 2
> > >         0xffff9965007e3c90     8863   reopen_file      UN 0  1:29:22.926
> > >   RWSEM_WAITING_FOR_WRITE
> > >         0xffff996500393e00     9802   ls               UN 0  1:17:26.700
> > >   RWSEM_WAITING_FOR_READ
> > >
> > >
> > > the owner of the inode.i_rwsem of the directory is:
> > >
> > > [0 00:00:00.109] [UN]  PID: 8856   TASK: ffff8c6914275d00  CPU: 3
> > > COMMAND: "reopen_file"
> > >  #0 [ffff99650065b828] __schedule at ffffffff9b6e6095
> > >  #1 [ffff99650065b8b8] schedule at ffffffff9b6e64df
> > >  #2 [ffff99650065b8c8] schedule_timeout at ffffffff9b6e9f89
> > >  #3 [ffff99650065b940] msleep at ffffffff9af573a9
> > >  #4 [ffff99650065b948] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> > >  #5 [ffff99650065ba38] cifs_writepage_locked at ffffffffc0a0b8f3 [cifs]
> > >  #6 [ffff99650065bab0] cifs_launder_page at ffffffffc0a0bb72 [cifs]
> > >  #7 [ffff99650065bb30] invalidate_inode_pages2_range at ffffffff9b04d4bd
> > >  #8 [ffff99650065bcb8] cifs_invalidate_mapping at ffffffffc0a11339 [cifs]
> > >  #9 [ffff99650065bcd0] cifs_revalidate_mapping at ffffffffc0a1139a [cifs]
> > > #10 [ffff99650065bcf0] cifs_d_revalidate at ffffffffc0a014f6 [cifs]
> > > #11 [ffff99650065bd08] path_openat at ffffffff9b0fe7f7
> > > #12 [ffff99650065bdd8] do_filp_open at ffffffff9b100a33
> > > #13 [ffff99650065bee0] do_sys_open at ffffffff9b0eb2d6
> > > #14 [ffff99650065bf38] do_syscall_64 at ffffffff9ae04315
> > >
> > > cifs_launder_page is for page 0xffffd1e2c07d2480
> > >
> > > crash> page.index,mapping,flags 0xffffd1e2c07d2480
> > >       index = 0x8
> > >       mapping = 0xffff8c68f3cd0db0
> > >   flags = 0xfffffc0008095
> > >
> > >   PAGE-FLAG       BIT  VALUE
> > >   PG_locked         0  0000001
> > >   PG_uptodate       2  0000004
> > >   PG_lru            4  0000010
> > >   PG_waiters        7  0000080
> > >   PG_writeback     15  0008000
> > >
> > >
> > > inode is ffff8c68f3cd0c40
> > > inode.i_rwsem is ffff8c68f3cd0ce0
> > >      DENTRY           INODE           SUPERBLK     TYPE PATH
> > > ffff8c68a1f1b480 ffff8c68f3cd0c40 ffff8c6915bf9000 REG
> > > /mnt/vm1_smb/testfile.8853
> > >
> > >
> > > this process holds the inode->i_rwsem for the parent directory, is
> > > laundering a page attached to the inode of the file it's opening, and in
> > > _cifsFileInfo_put is trying to down_write the cifsInodeInflock_sem
> > > for the file itself.
> > >
> > >
> > > <struct rw_semaphore 0xffff8c68f3cd0ce0>:
> > >         owner: <struct task_struct 0xffff8c6914272e80> (UN -   8854 -
> > > reopen_file), counter: 0x0000000000000003
> > >         waitlist: 1
> > >         0xffff9965005dfd80     8855   reopen_file      UN 0  1:29:22.912
> > >   RWSEM_WAITING_FOR_WRITE
> > >
> > > this is the inode.i_rwsem for the file
> > >
> > > the owner:
> > >
> > > [0 00:48:22.739] [UN]  PID: 8854   TASK: ffff8c6914272e80  CPU: 2
> > > COMMAND: "reopen_file"
> > >  #0 [ffff99650054fb38] __schedule at ffffffff9b6e6095
> > >  #1 [ffff99650054fbc8] schedule at ffffffff9b6e64df
> > >  #2 [ffff99650054fbd8] io_schedule at ffffffff9b6e68e2
> > >  #3 [ffff99650054fbe8] __lock_page at ffffffff9b03c56f
> > >  #4 [ffff99650054fc80] pagecache_get_page at ffffffff9b03dcdf
> > >  #5 [ffff99650054fcc0] grab_cache_page_write_begin at ffffffff9b03ef4c
> > >  #6 [ffff99650054fcd0] cifs_write_begin at ffffffffc0a064ec [cifs]
> > >  #7 [ffff99650054fd30] generic_perform_write at ffffffff9b03bba4
> > >  #8 [ffff99650054fda8] __generic_file_write_iter at ffffffff9b04060a
> > >  #9 [ffff99650054fdf0] cifs_strict_writev.cold.70 at ffffffffc0a4469b [cifs]
> > > #10 [ffff99650054fe48] new_sync_write at ffffffff9b0ec1dd
> > > #11 [ffff99650054fed0] vfs_write at ffffffff9b0eed35
> > > #12 [ffff99650054ff00] ksys_write at ffffffff9b0eefd9
> > > #13 [ffff99650054ff38] do_syscall_64 at ffffffff9ae04315
> > >
> > > the process holds the inode->i_rwsem for the file to which it's writing,
> > > and is trying to __lock_page for the same page as in the other processes
> > >
> > >
> > > the other tasks:
> > > [0 00:00:00.028] [UN]  PID: 8859   TASK: ffff8c6915479740  CPU: 2
> > > COMMAND: "reopen_file"
> > >  #0 [ffff9965007b39d8] __schedule at ffffffff9b6e6095
> > >  #1 [ffff9965007b3a68] schedule at ffffffff9b6e64df
> > >  #2 [ffff9965007b3a78] schedule_timeout at ffffffff9b6e9f89
> > >  #3 [ffff9965007b3af0] msleep at ffffffff9af573a9
> > >  #4 [ffff9965007b3af8] cifs_new_fileinfo.cold.61 at ffffffffc0a42a07 [cifs]
> > >  #5 [ffff9965007b3b78] cifs_open at ffffffffc0a0709d [cifs]
> > >  #6 [ffff9965007b3cd8] do_dentry_open at ffffffff9b0e9b7a
> > >  #7 [ffff9965007b3d08] path_openat at ffffffff9b0fe34f
> > >  #8 [ffff9965007b3dd8] do_filp_open at ffffffff9b100a33
> > >  #9 [ffff9965007b3ee0] do_sys_open at ffffffff9b0eb2d6
> > > #10 [ffff9965007b3f38] do_syscall_64 at ffffffff9ae04315
> > >
> > > this is opening the file, and is trying to down_write cinode->lock_sem
> > >
> > >
> > > [0 00:00:00.041] [UN]  PID: 8860   TASK: ffff8c691547ae80  CPU: 2
> > > COMMAND: "reopen_file"
> > > [0 00:00:00.057] [UN]  PID: 8861   TASK: ffff8c6915478000  CPU: 3
> > > COMMAND: "reopen_file"
> > > [0 00:00:00.059] [UN]  PID: 8858   TASK: ffff8c6914271740  CPU: 2
> > > COMMAND: "reopen_file"
> > > [0 00:00:00.109] [UN]  PID: 8862   TASK: ffff8c691547dd00  CPU: 6
> > > COMMAND: "reopen_file"
> > >  #0 [ffff9965007c3c78] __schedule at ffffffff9b6e6095
> > >  #1 [ffff9965007c3d08] schedule at ffffffff9b6e64df
> > >  #2 [ffff9965007c3d18] schedule_timeout at ffffffff9b6e9f89
> > >  #3 [ffff9965007c3d90] msleep at ffffffff9af573a9
> > >  #4 [ffff9965007c3d98] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> > >  #5 [ffff9965007c3e88] cifs_close at ffffffffc0a07aaf [cifs]
> > >  #6 [ffff9965007c3ea0] __fput at ffffffff9b0efa6e
> > >  #7 [ffff9965007c3ee8] task_work_run at ffffffff9aef1614
> > >  #8 [ffff9965007c3f20] exit_to_usermode_loop at ffffffff9ae03d6f
> > >  #9 [ffff9965007c3f38] do_syscall_64 at ffffffff9ae0444c
> > >
> > > closing the file, and trying to down_write cifsi->lock_sem
> > >
> > >
> > > [0 00:48:22.839] [UN]  PID: 8857   TASK: ffff8c6914270000  CPU: 7
> > > COMMAND: "reopen_file"
> > >  #0 [ffff9965006a7cc8] __schedule at ffffffff9b6e6095
> > >  #1 [ffff9965006a7d58] schedule at ffffffff9b6e64df
> > >  #2 [ffff9965006a7d68] io_schedule at ffffffff9b6e68e2
> > >  #3 [ffff9965006a7d78] wait_on_page_bit at ffffffff9b03cac6
> > >  #4 [ffff9965006a7e10] __filemap_fdatawait_range at ffffffff9b03b028
> > >  #5 [ffff9965006a7ed8] filemap_write_and_wait at ffffffff9b040165
> > >  #6 [ffff9965006a7ef0] cifs_flush at ffffffffc0a0c2fa [cifs]
> > >  #7 [ffff9965006a7f10] filp_close at ffffffff9b0e93f1
> > >  #8 [ffff9965006a7f30] __x64_sys_close at ffffffff9b0e9a0e
> > >  #9 [ffff9965006a7f38] do_syscall_64 at ffffffff9ae04315
> > >
> > > in __filemap_fdatawait_range
> > >                         wait_on_page_writeback(page);
> > > for the same page of the file
> > >
> > >
> > >
> > > [0 00:48:22.718] [UN]  PID: 8855   TASK: ffff8c69142745c0  CPU: 7
> > > COMMAND: "reopen_file"
> > >  #0 [ffff9965005dfc98] __schedule at ffffffff9b6e6095
> > >  #1 [ffff9965005dfd28] schedule at ffffffff9b6e64df
> > >  #2 [ffff9965005dfd38] rwsem_down_write_slowpath at ffffffff9af283d7
> > >  #3 [ffff9965005dfdf0] cifs_strict_writev at ffffffffc0a0c40a [cifs]
> > >  #4 [ffff9965005dfe48] new_sync_write at ffffffff9b0ec1dd
> > >  #5 [ffff9965005dfed0] vfs_write at ffffffff9b0eed35
> > >  #6 [ffff9965005dff00] ksys_write at ffffffff9b0eefd9
> > >  #7 [ffff9965005dff38] do_syscall_64 at ffffffff9ae04315
> > >
> > >         inode_lock(inode);
> > >
> > >
> > > and one 'ls' later on, to see whether the rest of the mount is available
> > > (the test file is in the root, so we get blocked up on the directory
> > > ->i_rwsem), so the entire mount is unavailable
> > >
> > > [0 00:36:26.473] [UN]  PID: 9802   TASK: ffff8c691436ae80  CPU: 4
> > > COMMAND: "ls"
> > >  #0 [ffff996500393d28] __schedule at ffffffff9b6e6095
> > >  #1 [ffff996500393db8] schedule at ffffffff9b6e64df
> > >  #2 [ffff996500393dc8] rwsem_down_read_slowpath at ffffffff9b6e9421
> > >  #3 [ffff996500393e78] down_read_killable at ffffffff9b6e95e2
> > >  #4 [ffff996500393e88] iterate_dir at ffffffff9b103c56
> > >  #5 [ffff996500393ec8] ksys_getdents64 at ffffffff9b104b0c
> > >  #6 [ffff996500393f30] __x64_sys_getdents64 at ffffffff9b104bb6
> > >  #7 [ffff996500393f38] do_syscall_64 at ffffffff9ae04315
> > >
> > > in iterate_dir:
> > >         if (shared)
> > >                 res = down_read_killable(&inode->i_rwsem);  <<<<
> > >         else
> > >                 res = down_write_killable(&inode->i_rwsem);
> > >
>
> Thanks for the update.
>
> I would suggest to shorten the description to include only two traces
> of deadlocked processes to improve readability. Please find my other
> comments below.
>
> >
> > Reported-by: Frank Sorenson <sorenson@redhat.com>:
> > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > ---
> >  fs/cifs/cifsfs.c   | 13 +++++++++-
> >  fs/cifs/cifsglob.h |  5 +++-
> >  fs/cifs/file.c     | 72 +++++++++++++++++++++++++++++++++++-------------------
> >  3 files changed, 63 insertions(+), 27 deletions(-)
> >
> > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > index e4e3b573d20c..f8e201c45ccb 100644
> > --- a/fs/cifs/cifsfs.c
> > +++ b/fs/cifs/cifsfs.c
> > @@ -119,6 +119,7 @@ extern mempool_t *cifs_mid_poolp;
> >
> >  struct workqueue_struct        *cifsiod_wq;
> >  struct workqueue_struct        *decrypt_wq;
> > +struct workqueue_struct        *fileinfo_put_wq;
> >  struct workqueue_struct        *cifsoplockd_wq;
> >  __u32 cifs_lock_secret;
> >
> > @@ -1557,11 +1558,18 @@ init_cifs(void)
> >                 goto out_destroy_cifsiod_wq;
> >         }
> >
> > +       fileinfo_put_wq = alloc_workqueue("cifsfileinfoput",
> > +                                    WQ_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> > +       if (!fileinfo_put_wq) {
> > +               rc = -ENOMEM;
> > +               goto out_destroy_decrypt_wq;
> > +       }
> > +
> >         cifsoplockd_wq = alloc_workqueue("cifsoplockd",
> >                                          WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> >         if (!cifsoplockd_wq) {
> >                 rc = -ENOMEM;
> > -               goto out_destroy_decrypt_wq;
> > +               goto out_destroy_fileinfo_put_wq;
> >         }
> >
> >         rc = cifs_fscache_register();
> > @@ -1627,6 +1635,8 @@ init_cifs(void)
> >         cifs_fscache_unregister();
> >  out_destroy_cifsoplockd_wq:
> >         destroy_workqueue(cifsoplockd_wq);
> > +out_destroy_fileinfo_put_wq:
> > +       destroy_workqueue(fileinfo_put_wq);
> >  out_destroy_decrypt_wq:
> >         destroy_workqueue(decrypt_wq);
> >  out_destroy_cifsiod_wq:
> > @@ -1656,6 +1666,7 @@ exit_cifs(void)
> >         cifs_fscache_unregister();
> >         destroy_workqueue(cifsoplockd_wq);
> >         destroy_workqueue(decrypt_wq);
> > +       destroy_workqueue(fileinfo_put_wq);
> >         destroy_workqueue(cifsiod_wq);
> >         cifs_proc_clean();
> >  }
> > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> > index d78bfcc19156..e0a7dc3f62b2 100644
> > --- a/fs/cifs/cifsglob.h
> > +++ b/fs/cifs/cifsglob.h
> > @@ -1265,6 +1265,7 @@ struct cifsFileInfo {
> >         struct mutex fh_mutex; /* prevents reopen race after dead ses*/
> >         struct cifs_search_info srch_inf;
> >         struct work_struct oplock_break; /* work for oplock breaks */
> > +       struct work_struct put; /* work for the final part of _put */
> >  };
> >
> >  struct cifs_io_parms {
> > @@ -1370,7 +1371,8 @@ cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
> >  }
> >
> >  struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
> > -void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr);
> > +void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr,
> > +                      bool offload);
>
> Do we still need wait_oplock_hdlr here? It is only being used in
> cifs_oplock_break() and it seems that we can easily remove it and just
> offload that occurrence to the worker thread archiving the same
> functionality.

True. Will do that change.

>
> >  void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
> >
> >  #define CIFS_CACHE_READ_FLG    1
> > @@ -1907,6 +1909,7 @@ void cifs_queue_oplock_break(struct cifsFileInfo *cfile);
> >  extern const struct slow_work_ops cifs_oplock_break_ops;
> >  extern struct workqueue_struct *cifsiod_wq;
> >  extern struct workqueue_struct *decrypt_wq;
> > +extern struct workqueue_struct *fileinfo_put_wq;
> >  extern struct workqueue_struct *cifsoplockd_wq;
> >  extern __u32 cifs_lock_secret;
> >
> > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> > index 67e7d0ffe385..309d6948d2f4 100644
> > --- a/fs/cifs/file.c
> > +++ b/fs/cifs/file.c
> > @@ -375,6 +375,41 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
> >         return cifs_file;
> >  }
> >
> > +static void cifsFileInfo_put_final(struct cifsFileInfo *cifs_file)
>
> This should work but I actually meant something different: to offload
> the whole _cifsFileInfo_put() by renaming it to
> cifsFileInfo_put_final() as is and adding new _cifsFileInfo_put() -
> see below.
>
> _cifsFileInfo_put(cifs_file, wait_oplock_handler, offload)
> {
>
> [ with optimizations ]
> // acquire only file info lock
> // check reference
> // if ref=1 and offload=True then put the work in the queue, drop the
> file info lock and exit
> // else if ref>1 then just decrement, drop the lock and exit - no need
> to take tcon and inode locks because we don't modify those lists
> // else (meaning ref=1 and offload=False) drop the file info lock and
> call cifsFileInfo_put_final()
>
> OR
>
> [ without optimizations ]
> // just use qeueue_work() all the time when offload=True
>
> }

We can't just unconditionally queue the work as in the "without
optimizations" example
because we only have a single work_struct which is part of the
cifsFileInfo structure.

We have to protect against the case where two thread call
cifsFileInfo_put() concurrently
and make sure we still only call queue_work() once, for the very last reference.

I think what my patch does is basically already the "with
optimizations" example above
but it also does some additional things before, conditionally, calling
_final() directly or via
a work queue.

It does:
1, check the reference, if >1 then decrement it and return immediately.
2,  some additional stuff while we are still holding the locks
3 if offload==true, invoke a work queue otherwise call _final() directly.


But I can move more of the "additional stuff" that it does into the
_final() function
and make it more similar to your suggestion.


>
> The reason why I think it's better is that we can make further use of
> it for BATCH oplocks implementation. In case of closing a file with
> BATCH oplock, we may change a function above to call mod_queue_work()
> with some timeout instead of queue_work(). Then another open call
> comes, looks up the cifsFileInfo structure in the open file list and
> increments the reference. By the time when the mod_queue_work timeout
> expires and the worker thread decrements the reference it will remain
> positive thus available for the existing and other open calls to use:
>
> Example of possible execution:
>
> 0s T1 opens a file and gets BATCH oplock - reference is 1;
> 1s T1 closes the file by calling cifsFileInfo_put(cfile, true, true)
> and put cifsFileInfo in the work queue with 10s timeout;
> 2s T1 opens the same file, looks it up in the open file list and
> increment the reference to 2;
> ...
> 11s T2 pulls cifsFileInfo from the work queue, calls and decrement the
> reference to 1;
> 12s T2 closes the file and put cifsFileInfo in the work queue with 10s timeout;
> ...
> 22s T3 pulls cifsFileInfo from the work queue, decrements the
> reference to 0 and does all the cleanup steps from
> cifsFileInfo_put_final().
>
> This should significantly improve performance of applications that do
> many open-close calls on the same file and it won't require a lot of
> code changes.
>
> The above suggestions (to offload the whole _cifsFileInfo_put) doesn't
> seem like a big change to your current patch but it also may be done
> as a followup patch, so, leaving it up to you What do you think?

I will do that change and re-send
Thanks!

>
> --
> Best regards,
> Pavel Shilovsky

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH] cifs: move cifsFileInfo_put logic into a work-queue
  2019-10-30  1:25     ` ronnie sahlberg
@ 2019-10-30 15:57       ` Pavel Shilovsky
  0 siblings, 0 replies; 9+ messages in thread
From: Pavel Shilovsky @ 2019-10-30 15:57 UTC (permalink / raw)
  To: ronnie sahlberg; +Cc: Ronnie Sahlberg, linux-cifs

вт, 29 окт. 2019 г. в 18:25, ronnie sahlberg <ronniesahlberg@gmail.com>:
>
> On Wed, Oct 30, 2019 at 9:22 AM Pavel Shilovsky <piastryyy@gmail.com> wrote:
> >
> > вт, 29 окт. 2019 г. в 00:25, Ronnie Sahlberg <lsahlber@redhat.com>:
> > >
> > > This patch moves the final part of the cifsFileInfo_put() logic where we
> > > need a write lock on lock_sem to be processed in a separate thread that
> > > holds no other locks.
> > > This is to prevent deadlocks like the one below:
> > >
> > > > there are 6 processes looping to while trying to down_write
> > > > cinode->lock_sem, 5 of them from _cifsFileInfo_put, and one from
> > > > cifs_new_fileinfo
> > > >
> > > > and there are 5 other processes which are blocked, several of them
> > > > waiting on either PG_writeback or PG_locked (which are both set), all
> > > > for the same page of the file
> > > >
> > > > 2 inode_lock() (inode->i_rwsem) for the file
> > > > 1 wait_on_page_writeback() for the page
> > > > 1 down_read(inode->i_rwsem) for the inode of the directory
> > > > 1 inode_lock()(inode->i_rwsem) for the inode of the directory
> > > > 1 __lock_page
> > > >
> > > >
> > > > so processes are blocked waiting on:
> > > >   page flags PG_locked and PG_writeback for one specific page
> > > >   inode->i_rwsem for the directory
> > > >   inode->i_rwsem for the file
> > > >   cifsInodeInflock_sem
> > > >
> > > >
> > > >
> > > > here are the more gory details (let me know if I need to provide
> > > > anything more/better):
> > > >
> > > > [0 00:48:22.765] [UN]  PID: 8863   TASK: ffff8c691547c5c0  CPU: 3
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff9965007e3ba8] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff9965007e3c38] schedule at ffffffff9b6e64df
> > > >  #2 [ffff9965007e3c48] rwsem_down_write_slowpath at ffffffff9af283d7
> > > >  #3 [ffff9965007e3cb8] legitimize_path at ffffffff9b0f975d
> > > >  #4 [ffff9965007e3d08] path_openat at ffffffff9b0fe55d
> > > >  #5 [ffff9965007e3dd8] do_filp_open at ffffffff9b100a33
> > > >  #6 [ffff9965007e3ee0] do_sys_open at ffffffff9b0eb2d6
> > > >  #7 [ffff9965007e3f38] do_syscall_64 at ffffffff9ae04315
> > > > * (I think legitimize_path is bogus)
> > > >
> > > > in path_openat
> > > >         } else {
> > > >                 const char *s = path_init(nd, flags);
> > > >                 while (!(error = link_path_walk(s, nd)) &&
> > > >                         (error = do_last(nd, file, op)) > 0) {  <<<<
> > > >
> > > > do_last:
> > > >         if (open_flag & O_CREAT)
> > > >                 inode_lock(dir->d_inode);  <<<<
> > > >         else
> > > > so it's trying to take inode->i_rwsem for the directory
> > > >
> > > >      DENTRY           INODE           SUPERBLK     TYPE PATH
> > > > ffff8c68bb8e79c0 ffff8c691158ef20 ffff8c6915bf9000 DIR  /mnt/vm1_smb/
> > > > inode.i_rwsem is ffff8c691158efc0
> > > >
> > > > <struct rw_semaphore 0xffff8c691158efc0>:
> > > >         owner: <struct task_struct 0xffff8c6914275d00> (UN -   8856 -
> > > > reopen_file), counter: 0x0000000000000003
> > > >         waitlist: 2
> > > >         0xffff9965007e3c90     8863   reopen_file      UN 0  1:29:22.926
> > > >   RWSEM_WAITING_FOR_WRITE
> > > >         0xffff996500393e00     9802   ls               UN 0  1:17:26.700
> > > >   RWSEM_WAITING_FOR_READ
> > > >
> > > >
> > > > the owner of the inode.i_rwsem of the directory is:
> > > >
> > > > [0 00:00:00.109] [UN]  PID: 8856   TASK: ffff8c6914275d00  CPU: 3
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff99650065b828] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff99650065b8b8] schedule at ffffffff9b6e64df
> > > >  #2 [ffff99650065b8c8] schedule_timeout at ffffffff9b6e9f89
> > > >  #3 [ffff99650065b940] msleep at ffffffff9af573a9
> > > >  #4 [ffff99650065b948] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> > > >  #5 [ffff99650065ba38] cifs_writepage_locked at ffffffffc0a0b8f3 [cifs]
> > > >  #6 [ffff99650065bab0] cifs_launder_page at ffffffffc0a0bb72 [cifs]
> > > >  #7 [ffff99650065bb30] invalidate_inode_pages2_range at ffffffff9b04d4bd
> > > >  #8 [ffff99650065bcb8] cifs_invalidate_mapping at ffffffffc0a11339 [cifs]
> > > >  #9 [ffff99650065bcd0] cifs_revalidate_mapping at ffffffffc0a1139a [cifs]
> > > > #10 [ffff99650065bcf0] cifs_d_revalidate at ffffffffc0a014f6 [cifs]
> > > > #11 [ffff99650065bd08] path_openat at ffffffff9b0fe7f7
> > > > #12 [ffff99650065bdd8] do_filp_open at ffffffff9b100a33
> > > > #13 [ffff99650065bee0] do_sys_open at ffffffff9b0eb2d6
> > > > #14 [ffff99650065bf38] do_syscall_64 at ffffffff9ae04315
> > > >
> > > > cifs_launder_page is for page 0xffffd1e2c07d2480
> > > >
> > > > crash> page.index,mapping,flags 0xffffd1e2c07d2480
> > > >       index = 0x8
> > > >       mapping = 0xffff8c68f3cd0db0
> > > >   flags = 0xfffffc0008095
> > > >
> > > >   PAGE-FLAG       BIT  VALUE
> > > >   PG_locked         0  0000001
> > > >   PG_uptodate       2  0000004
> > > >   PG_lru            4  0000010
> > > >   PG_waiters        7  0000080
> > > >   PG_writeback     15  0008000
> > > >
> > > >
> > > > inode is ffff8c68f3cd0c40
> > > > inode.i_rwsem is ffff8c68f3cd0ce0
> > > >      DENTRY           INODE           SUPERBLK     TYPE PATH
> > > > ffff8c68a1f1b480 ffff8c68f3cd0c40 ffff8c6915bf9000 REG
> > > > /mnt/vm1_smb/testfile.8853
> > > >
> > > >
> > > > this process holds the inode->i_rwsem for the parent directory, is
> > > > laundering a page attached to the inode of the file it's opening, and in
> > > > _cifsFileInfo_put is trying to down_write the cifsInodeInflock_sem
> > > > for the file itself.
> > > >
> > > >
> > > > <struct rw_semaphore 0xffff8c68f3cd0ce0>:
> > > >         owner: <struct task_struct 0xffff8c6914272e80> (UN -   8854 -
> > > > reopen_file), counter: 0x0000000000000003
> > > >         waitlist: 1
> > > >         0xffff9965005dfd80     8855   reopen_file      UN 0  1:29:22.912
> > > >   RWSEM_WAITING_FOR_WRITE
> > > >
> > > > this is the inode.i_rwsem for the file
> > > >
> > > > the owner:
> > > >
> > > > [0 00:48:22.739] [UN]  PID: 8854   TASK: ffff8c6914272e80  CPU: 2
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff99650054fb38] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff99650054fbc8] schedule at ffffffff9b6e64df
> > > >  #2 [ffff99650054fbd8] io_schedule at ffffffff9b6e68e2
> > > >  #3 [ffff99650054fbe8] __lock_page at ffffffff9b03c56f
> > > >  #4 [ffff99650054fc80] pagecache_get_page at ffffffff9b03dcdf
> > > >  #5 [ffff99650054fcc0] grab_cache_page_write_begin at ffffffff9b03ef4c
> > > >  #6 [ffff99650054fcd0] cifs_write_begin at ffffffffc0a064ec [cifs]
> > > >  #7 [ffff99650054fd30] generic_perform_write at ffffffff9b03bba4
> > > >  #8 [ffff99650054fda8] __generic_file_write_iter at ffffffff9b04060a
> > > >  #9 [ffff99650054fdf0] cifs_strict_writev.cold.70 at ffffffffc0a4469b [cifs]
> > > > #10 [ffff99650054fe48] new_sync_write at ffffffff9b0ec1dd
> > > > #11 [ffff99650054fed0] vfs_write at ffffffff9b0eed35
> > > > #12 [ffff99650054ff00] ksys_write at ffffffff9b0eefd9
> > > > #13 [ffff99650054ff38] do_syscall_64 at ffffffff9ae04315
> > > >
> > > > the process holds the inode->i_rwsem for the file to which it's writing,
> > > > and is trying to __lock_page for the same page as in the other processes
> > > >
> > > >
> > > > the other tasks:
> > > > [0 00:00:00.028] [UN]  PID: 8859   TASK: ffff8c6915479740  CPU: 2
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff9965007b39d8] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff9965007b3a68] schedule at ffffffff9b6e64df
> > > >  #2 [ffff9965007b3a78] schedule_timeout at ffffffff9b6e9f89
> > > >  #3 [ffff9965007b3af0] msleep at ffffffff9af573a9
> > > >  #4 [ffff9965007b3af8] cifs_new_fileinfo.cold.61 at ffffffffc0a42a07 [cifs]
> > > >  #5 [ffff9965007b3b78] cifs_open at ffffffffc0a0709d [cifs]
> > > >  #6 [ffff9965007b3cd8] do_dentry_open at ffffffff9b0e9b7a
> > > >  #7 [ffff9965007b3d08] path_openat at ffffffff9b0fe34f
> > > >  #8 [ffff9965007b3dd8] do_filp_open at ffffffff9b100a33
> > > >  #9 [ffff9965007b3ee0] do_sys_open at ffffffff9b0eb2d6
> > > > #10 [ffff9965007b3f38] do_syscall_64 at ffffffff9ae04315
> > > >
> > > > this is opening the file, and is trying to down_write cinode->lock_sem
> > > >
> > > >
> > > > [0 00:00:00.041] [UN]  PID: 8860   TASK: ffff8c691547ae80  CPU: 2
> > > > COMMAND: "reopen_file"
> > > > [0 00:00:00.057] [UN]  PID: 8861   TASK: ffff8c6915478000  CPU: 3
> > > > COMMAND: "reopen_file"
> > > > [0 00:00:00.059] [UN]  PID: 8858   TASK: ffff8c6914271740  CPU: 2
> > > > COMMAND: "reopen_file"
> > > > [0 00:00:00.109] [UN]  PID: 8862   TASK: ffff8c691547dd00  CPU: 6
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff9965007c3c78] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff9965007c3d08] schedule at ffffffff9b6e64df
> > > >  #2 [ffff9965007c3d18] schedule_timeout at ffffffff9b6e9f89
> > > >  #3 [ffff9965007c3d90] msleep at ffffffff9af573a9
> > > >  #4 [ffff9965007c3d98] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> > > >  #5 [ffff9965007c3e88] cifs_close at ffffffffc0a07aaf [cifs]
> > > >  #6 [ffff9965007c3ea0] __fput at ffffffff9b0efa6e
> > > >  #7 [ffff9965007c3ee8] task_work_run at ffffffff9aef1614
> > > >  #8 [ffff9965007c3f20] exit_to_usermode_loop at ffffffff9ae03d6f
> > > >  #9 [ffff9965007c3f38] do_syscall_64 at ffffffff9ae0444c
> > > >
> > > > closing the file, and trying to down_write cifsi->lock_sem
> > > >
> > > >
> > > > [0 00:48:22.839] [UN]  PID: 8857   TASK: ffff8c6914270000  CPU: 7
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff9965006a7cc8] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff9965006a7d58] schedule at ffffffff9b6e64df
> > > >  #2 [ffff9965006a7d68] io_schedule at ffffffff9b6e68e2
> > > >  #3 [ffff9965006a7d78] wait_on_page_bit at ffffffff9b03cac6
> > > >  #4 [ffff9965006a7e10] __filemap_fdatawait_range at ffffffff9b03b028
> > > >  #5 [ffff9965006a7ed8] filemap_write_and_wait at ffffffff9b040165
> > > >  #6 [ffff9965006a7ef0] cifs_flush at ffffffffc0a0c2fa [cifs]
> > > >  #7 [ffff9965006a7f10] filp_close at ffffffff9b0e93f1
> > > >  #8 [ffff9965006a7f30] __x64_sys_close at ffffffff9b0e9a0e
> > > >  #9 [ffff9965006a7f38] do_syscall_64 at ffffffff9ae04315
> > > >
> > > > in __filemap_fdatawait_range
> > > >                         wait_on_page_writeback(page);
> > > > for the same page of the file
> > > >
> > > >
> > > >
> > > > [0 00:48:22.718] [UN]  PID: 8855   TASK: ffff8c69142745c0  CPU: 7
> > > > COMMAND: "reopen_file"
> > > >  #0 [ffff9965005dfc98] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff9965005dfd28] schedule at ffffffff9b6e64df
> > > >  #2 [ffff9965005dfd38] rwsem_down_write_slowpath at ffffffff9af283d7
> > > >  #3 [ffff9965005dfdf0] cifs_strict_writev at ffffffffc0a0c40a [cifs]
> > > >  #4 [ffff9965005dfe48] new_sync_write at ffffffff9b0ec1dd
> > > >  #5 [ffff9965005dfed0] vfs_write at ffffffff9b0eed35
> > > >  #6 [ffff9965005dff00] ksys_write at ffffffff9b0eefd9
> > > >  #7 [ffff9965005dff38] do_syscall_64 at ffffffff9ae04315
> > > >
> > > >         inode_lock(inode);
> > > >
> > > >
> > > > and one 'ls' later on, to see whether the rest of the mount is available
> > > > (the test file is in the root, so we get blocked up on the directory
> > > > ->i_rwsem), so the entire mount is unavailable
> > > >
> > > > [0 00:36:26.473] [UN]  PID: 9802   TASK: ffff8c691436ae80  CPU: 4
> > > > COMMAND: "ls"
> > > >  #0 [ffff996500393d28] __schedule at ffffffff9b6e6095
> > > >  #1 [ffff996500393db8] schedule at ffffffff9b6e64df
> > > >  #2 [ffff996500393dc8] rwsem_down_read_slowpath at ffffffff9b6e9421
> > > >  #3 [ffff996500393e78] down_read_killable at ffffffff9b6e95e2
> > > >  #4 [ffff996500393e88] iterate_dir at ffffffff9b103c56
> > > >  #5 [ffff996500393ec8] ksys_getdents64 at ffffffff9b104b0c
> > > >  #6 [ffff996500393f30] __x64_sys_getdents64 at ffffffff9b104bb6
> > > >  #7 [ffff996500393f38] do_syscall_64 at ffffffff9ae04315
> > > >
> > > > in iterate_dir:
> > > >         if (shared)
> > > >                 res = down_read_killable(&inode->i_rwsem);  <<<<
> > > >         else
> > > >                 res = down_write_killable(&inode->i_rwsem);
> > > >
> >
> > Thanks for the update.
> >
> > I would suggest to shorten the description to include only two traces
> > of deadlocked processes to improve readability. Please find my other
> > comments below.
> >
> > >
> > > Reported-by: Frank Sorenson <sorenson@redhat.com>:
> > > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > > ---
> > >  fs/cifs/cifsfs.c   | 13 +++++++++-
> > >  fs/cifs/cifsglob.h |  5 +++-
> > >  fs/cifs/file.c     | 72 +++++++++++++++++++++++++++++++++++-------------------
> > >  3 files changed, 63 insertions(+), 27 deletions(-)
> > >
> > > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > > index e4e3b573d20c..f8e201c45ccb 100644
> > > --- a/fs/cifs/cifsfs.c
> > > +++ b/fs/cifs/cifsfs.c
> > > @@ -119,6 +119,7 @@ extern mempool_t *cifs_mid_poolp;
> > >
> > >  struct workqueue_struct        *cifsiod_wq;
> > >  struct workqueue_struct        *decrypt_wq;
> > > +struct workqueue_struct        *fileinfo_put_wq;
> > >  struct workqueue_struct        *cifsoplockd_wq;
> > >  __u32 cifs_lock_secret;
> > >
> > > @@ -1557,11 +1558,18 @@ init_cifs(void)
> > >                 goto out_destroy_cifsiod_wq;
> > >         }
> > >
> > > +       fileinfo_put_wq = alloc_workqueue("cifsfileinfoput",
> > > +                                    WQ_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> > > +       if (!fileinfo_put_wq) {
> > > +               rc = -ENOMEM;
> > > +               goto out_destroy_decrypt_wq;
> > > +       }
> > > +
> > >         cifsoplockd_wq = alloc_workqueue("cifsoplockd",
> > >                                          WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> > >         if (!cifsoplockd_wq) {
> > >                 rc = -ENOMEM;
> > > -               goto out_destroy_decrypt_wq;
> > > +               goto out_destroy_fileinfo_put_wq;
> > >         }
> > >
> > >         rc = cifs_fscache_register();
> > > @@ -1627,6 +1635,8 @@ init_cifs(void)
> > >         cifs_fscache_unregister();
> > >  out_destroy_cifsoplockd_wq:
> > >         destroy_workqueue(cifsoplockd_wq);
> > > +out_destroy_fileinfo_put_wq:
> > > +       destroy_workqueue(fileinfo_put_wq);
> > >  out_destroy_decrypt_wq:
> > >         destroy_workqueue(decrypt_wq);
> > >  out_destroy_cifsiod_wq:
> > > @@ -1656,6 +1666,7 @@ exit_cifs(void)
> > >         cifs_fscache_unregister();
> > >         destroy_workqueue(cifsoplockd_wq);
> > >         destroy_workqueue(decrypt_wq);
> > > +       destroy_workqueue(fileinfo_put_wq);
> > >         destroy_workqueue(cifsiod_wq);
> > >         cifs_proc_clean();
> > >  }
> > > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> > > index d78bfcc19156..e0a7dc3f62b2 100644
> > > --- a/fs/cifs/cifsglob.h
> > > +++ b/fs/cifs/cifsglob.h
> > > @@ -1265,6 +1265,7 @@ struct cifsFileInfo {
> > >         struct mutex fh_mutex; /* prevents reopen race after dead ses*/
> > >         struct cifs_search_info srch_inf;
> > >         struct work_struct oplock_break; /* work for oplock breaks */
> > > +       struct work_struct put; /* work for the final part of _put */
> > >  };
> > >
> > >  struct cifs_io_parms {
> > > @@ -1370,7 +1371,8 @@ cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
> > >  }
> > >
> > >  struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
> > > -void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr);
> > > +void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr,
> > > +                      bool offload);
> >
> > Do we still need wait_oplock_hdlr here? It is only being used in
> > cifs_oplock_break() and it seems that we can easily remove it and just
> > offload that occurrence to the worker thread archiving the same
> > functionality.
>
> True. Will do that change.
>
> >
> > >  void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
> > >
> > >  #define CIFS_CACHE_READ_FLG    1
> > > @@ -1907,6 +1909,7 @@ void cifs_queue_oplock_break(struct cifsFileInfo *cfile);
> > >  extern const struct slow_work_ops cifs_oplock_break_ops;
> > >  extern struct workqueue_struct *cifsiod_wq;
> > >  extern struct workqueue_struct *decrypt_wq;
> > > +extern struct workqueue_struct *fileinfo_put_wq;
> > >  extern struct workqueue_struct *cifsoplockd_wq;
> > >  extern __u32 cifs_lock_secret;
> > >
> > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> > > index 67e7d0ffe385..309d6948d2f4 100644
> > > --- a/fs/cifs/file.c
> > > +++ b/fs/cifs/file.c
> > > @@ -375,6 +375,41 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
> > >         return cifs_file;
> > >  }
> > >
> > > +static void cifsFileInfo_put_final(struct cifsFileInfo *cifs_file)
> >
> > This should work but I actually meant something different: to offload
> > the whole _cifsFileInfo_put() by renaming it to
> > cifsFileInfo_put_final() as is and adding new _cifsFileInfo_put() -
> > see below.
> >
> > _cifsFileInfo_put(cifs_file, wait_oplock_handler, offload)
> > {
> >
> > [ with optimizations ]
> > // acquire only file info lock
> > // check reference
> > // if ref=1 and offload=True then put the work in the queue, drop the
> > file info lock and exit
> > // else if ref>1 then just decrement, drop the lock and exit - no need
> > to take tcon and inode locks because we don't modify those lists
> > // else (meaning ref=1 and offload=False) drop the file info lock and
> > call cifsFileInfo_put_final()
> >
> > OR
> >
> > [ without optimizations ]
> > // just use qeueue_work() all the time when offload=True
> >
> > }
>
> We can't just unconditionally queue the work as in the "without
> optimizations" example
> because we only have a single work_struct which is part of the
> cifsFileInfo structure.

Yes, you are right. The subsequent one won't be queued.

This actually worries me about the current approach I suggested: if
the file was referenced just after we checked for ref > 1 but before
delayed work proceeded it would lead to work being submitted while
another thread holding a another reference. When that other thread
tries to put its reference, it will try to queue the work again but it
couldn't because another one is already there. This will lead to a
handle leak.


>
> We have to protect against the case where two thread call
> cifsFileInfo_put() concurrently
> and make sure we still only call queue_work() once, for the very last reference.
>
> I think what my patch does is basically already the "with
> optimizations" example above
> but it also does some additional things before, conditionally, calling
> _final() directly or via
> a work queue.
>
> It does:
> 1, check the reference, if >1 then decrement it and return immediately.
> 2,  some additional stuff while we are still holding the locks
> 3 if offload==true, invoke a work queue otherwise call _final() directly.
>
>
> But I can move more of the "additional stuff" that it does into the
> _final() function
> and make it more similar to your suggestion.
>

Thanks for doing that!

--
Best regards,
Pavel Shilovsky

^ permalink raw reply	[flat|nested] 9+ messages in thread

* [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue
@ 2019-10-30  2:59 " Ronnie Sahlberg
  0 siblings, 0 replies; 9+ messages in thread
From: Ronnie Sahlberg @ 2019-10-30  2:59 UTC (permalink / raw)
  To: linux-cifs

Pavel, 
version 3 of the patch with your suggestions.
I left the full commit message of the deadlocked threads as is though.



^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue
  2019-10-27 23:52 ` Frank Sorenson
@ 2019-10-28 22:51   ` Pavel Shilovsky
  0 siblings, 0 replies; 9+ messages in thread
From: Pavel Shilovsky @ 2019-10-28 22:51 UTC (permalink / raw)
  To: Frank Sorenson; +Cc: Ronnie Sahlberg, linux-cifs

пн, 28 окт. 2019 г. в 05:13, Frank Sorenson <sorenson@redhat.com>:
>
> On 10/26/19 4:04 PM, Ronnie Sahlberg wrote:
> > Steve, Pavel, Frank
> >
> > This patch moves the logic in cifsFileInfo_put() into a work-queue so that
> > it will be processed in a different thread which, importantly, does not hold
> > any other locks.
> >
> > This should address the deadlock that Frank reported in the thread:
> > Yet another hang after network disruption or smb restart -- multiple file writers
>
> Pavel,
>
> Thanks for understanding my report and translating it into what it meant.
>
> Ronnie,
> Thanks for the patch.  I'm happy to say that my attempt at the same
> looks like it would have been similar, had I known what I was doing to
> begin with :)
>
>
> Unfortunately, I think the patch really only moves the problem from one
> place to another.  I'm guessing that means we have a second underlying
> deadlock.  (this reproducer appears to be quite effective)
>
>
> On the plus side, only the one file involved is jammed in the deadlock
> now, as opposed to the parent directory as well, so it is at least progress.
>

Hi Frank, Ronnie,

Ok, it seems there is another bug resulting in a deadlock between a
page lock and writeback (WB) flag in cifs_writev_complete and
cifs_writepages.

1) cifs_writev_complete. in the case of WB_SYNC_ALL and EAGAIN
(reconnect) it calls cifs_writev_requeue. At this point it still has
WB flag set for all the pages being retried. Inside
cifs_writev_requeue it tries to lock the page:

kworker/4:3+cifsiod
#0 __schedule at ffffffffab4f1a45
#1 schedule at ffffffffab4f1ea0
#2 io_schedule at ffffffffab4f22a2
#3 __lock_page at ffffffffaae3f66f
#4 cifs_writev_complete at ffffffffc07df762
#5 process_one_work at ffffffffaacecc11
#6 worker_thread at ffffffffaaced0f0
#7 kthread at ffffffffaacf2ac2
#8 ret_from_fork at ffffffffab600215

2) cifs_writepages. It locks the page and then waits on WB flag to be
cleared before processing pages:

1 openloop.sh
#0 __schedule at ffffffffab4f1a45
#1 schedule at ffffffffab4f1ea0
#2 io_schedule at ffffffffab4f22a2
#3 wait_on_page_bit at ffffffffaae3fbc6
#4 cifs_writepages at ffffffffc07ffc73
#5 do_writepages at ffffffffaae4ba71
#6 __filemap_fdatawrite_range at ffffffffaae4321b
#7 filemap_write_and_wait at ffffffffaae432aa
#8 cifs_flush at ffffffffc0800fe3
#9 filp_close at ffffffffaaeed181
#10 do_dup2 at ffffffffaaf12c0b
#11 __x64_sys_dup2 at ffffffffaaf1306a
#12 do_syscall_64 at ffffffffaac04345

The bug is in cifs_writev_complete and cifs_writev_requeue: the 1st
needs to clear the WB flag and re-dirty pages before trying to retry
the IO; the 2nd needs additionally to skip pages that are no longer
dirty (e.g. written by another thread) and re-set the WB flag before
sending pages over the wire.

--
Best regards,
Pavel Shilovsky

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue
  2019-10-26 21:04 Ronnie Sahlberg
@ 2019-10-27 23:52 ` Frank Sorenson
  2019-10-28 22:51   ` Pavel Shilovsky
  0 siblings, 1 reply; 9+ messages in thread
From: Frank Sorenson @ 2019-10-27 23:52 UTC (permalink / raw)
  To: Ronnie Sahlberg, linux-cifs

On 10/26/19 4:04 PM, Ronnie Sahlberg wrote:
> Steve, Pavel, Frank
> 
> This patch moves the logic in cifsFileInfo_put() into a work-queue so that
> it will be processed in a different thread which, importantly, does not hold
> any other locks.
> 
> This should address the deadlock that Frank reported in the thread:
> Yet another hang after network disruption or smb restart -- multiple file writers

Pavel,

Thanks for understanding my report and translating it into what it meant.

Ronnie,
Thanks for the patch.  I'm happy to say that my attempt at the same
looks like it would have been similar, had I known what I was doing to
begin with :)


Unfortunately, I think the patch really only moves the problem from one
place to another.  I'm guessing that means we have a second underlying
deadlock.  (this reproducer appears to be quite effective)


On the plus side, only the one file involved is jammed in the deadlock
now, as opposed to the parent directory as well, so it is at least progress.


#!/bin/bash

testfile=testfile
openloop() {
        while true ; do
                exec 10<>$testfile
                <&10 >/dev/null
                echo "testing $$" >&10
                exec 10>&-
        done
}
for i in {1..50} ; do
        openloop &
done
wait


and on the server (once):
# systemctl restart smb.service
(or anything else which forces a reconnect)


After doing the above with 20 child processes, all are now blocked, as
are 3 cifsfileinfoput kworkers, a cifsiod kworker, and a flush-cifs kworker:


# ps x | awk '{if (substr($3, 1, 1) == "D"){print $3,$NF}}' | sort  |
uniq -c | sort -rn
     20 D /var/tmp/openloop.sh
      1 D [kworker/u16:9+cifsfileinfoput]
      1 D [kworker/u16:8+cifsfileinfoput]
      1 D [kworker/u16:25+flush-cifs-1]
      1 D [kworker/u16:19+cifsfileinfoput]
      1 D [kworker/4:3+cifsiod]


12 of the openloop.sh processes:
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 rwsem_down_write_slowpath at ffffffffaad29a47
	#3 cifs_strict_writev at ffffffffc08010e2
	#4 new_sync_write at ffffffffaaeeff6d
	#5 vfs_write at ffffffffaaef2ac5
	#6 ksys_write at ffffffffaaef2d69
	#7 do_syscall_64 at ffffffffaac04345
in cifs_strict_writev:
        inode_lock(inode);


3 openloop.sh:
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 schedule_timeout at ffffffffab4f5949
	#3 msleep at ffffffffaad58d89
	#4 cifs_down_write at ffffffffc07fa2b5
	#5 cifs_new_fileinfo at ffffffffc07fa392
	#6 cifs_open at ffffffffc07fae1f
	#7 do_dentry_open at ffffffffaaeed90a
	#8 path_openat at ffffffffaaf0204a
	#9 do_filp_open at ffffffffaaf04753
	#10 do_sys_open at ffffffffaaeef066
	#11 do_syscall_64 at ffffffffaac04345



3 openloop.sh
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 io_schedule at ffffffffab4f22a2
	#3 wait_on_page_bit at ffffffffaae3fbc6
	#4 __filemap_fdatawait_range at ffffffffaae3e158
	#5 filemap_write_and_wait at ffffffffaae432c5
	#6 cifs_flush at ffffffffc0800fe3
	#7 filp_close at ffffffffaaeed181
	#8 do_dup2 at ffffffffaaf12c0b
	#9 __x64_sys_dup2 at ffffffffaaf1306a
	#10 do_syscall_64 at ffffffffaac04345

in __filemap_fdatawait_range:
	wait_on_page_writeback(page);



1 openloop.sh
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 io_schedule at ffffffffab4f22a2
	#3 wait_on_page_bit at ffffffffaae3fbc6
	#4 cifs_writepages at ffffffffc07ffc73
	#5 do_writepages at ffffffffaae4ba71
	#6 __filemap_fdatawrite_range at ffffffffaae4321b
	#7 filemap_write_and_wait at ffffffffaae432aa
	#8 cifs_flush at ffffffffc0800fe3
	#9 filp_close at ffffffffaaeed181
	#10 do_dup2 at ffffffffaaf12c0b
	#11 __x64_sys_dup2 at ffffffffaaf1306a
	#12 do_syscall_64 at ffffffffaac04345

in cifs_writepages, we're really in wdata_prepare_pages
                if (wbc->sync_mode != WB_SYNC_NONE)
                        wait_on_page_writeback(page);

1 openloop.sh
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 io_schedule at ffffffffab4f22a2
	#3 __lock_page at ffffffffaae3f66f
	#4 pagecache_get_page at ffffffffaae40ddf
	#5 grab_cache_page_write_begin at ffffffffaae420ac
	#6 cifs_write_begin at ffffffffc07f9ea9
	#7 generic_perform_write at ffffffffaae3eca4
	#8 __generic_file_write_iter at ffffffffaae4376a
	#9 cifs_strict_writev at ffffffffc08011cf
	#10 new_sync_write at ffffffffaaeeff6d
	#11 vfs_write at ffffffffaaef2ac5
	#12 ksys_write at ffffffffaaef2d69
	#13 do_syscall_64 at ffffffffaac04345



kworker/u16:8+cifsfileinfoput
kworker/u16:19+cifsfileinfoput
kworker/u16:9+cifsfileinfoput
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 schedule_timeout at ffffffffab4f5949
	#3 msleep at ffffffffaad58d89
	#4 cifs_down_write at ffffffffc07fa2b5
	#5 _cifsFileInfo_put_work at ffffffffc07fb687
	#6 cifsFileInfo_put_work at ffffffffc07fd816
	#7 process_one_work at ffffffffaacecc11
	#8 worker_thread at ffffffffaaced0f0
	#9 kthread at ffffffffaacf2ac2
	#10 ret_from_fork at ffffffffab600215

kworker/4:3+cifsiod
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 io_schedule at ffffffffab4f22a2
	#3 __lock_page at ffffffffaae3f66f
	#4 cifs_writev_complete at ffffffffc07df762
	#5 process_one_work at ffffffffaacecc11
	#6 worker_thread at ffffffffaaced0f0
	#7 kthread at ffffffffaacf2ac2
	#8 ret_from_fork at ffffffffab600215

kworker/u16:25+flush-cifs-1
	#0 __schedule at ffffffffab4f1a45
	#1 schedule at ffffffffab4f1ea0
	#2 io_schedule at ffffffffab4f22a2
	#3 __lock_page at ffffffffaae3f66f
	#4 cifs_writepages at ffffffffc07ffcbe
	#5 do_writepages at ffffffffaae4ba71
	#6 __writeback_single_inode at ffffffffaaf25bdd
	#7 writeback_sb_inodes at ffffffffaaf26315
	#8 __writeback_inodes_wb at ffffffffaaf2660d
	#9 wb_writeback at ffffffffaaf2698f
	#10 wb_workfn at ffffffffaaf279cf
	#11 process_one_work at ffffffffaacecc11
	#12 worker_thread at ffffffffaaced0f0
	#13 kthread at ffffffffaacf2ac2
	#14 ret_from_fork at ffffffffab600215


the page which processes are either trying to lock or are waiting on
writeback:
FLAGS: fffffc000809d
  PAGE-FLAG       BIT  VALUE
  PG_locked         0  0000001
  PG_uptodate       2  0000004
  PG_dirty          3  0000008
  PG_lru            4  0000010
  PG_waiters        7  0000080
  PG_writeback     15  0008000
  PG_savepinned     3  0000008





Frank
--
Frank Sorenson
sorenson@redhat.com
Principal Software Maintenance Engineer
Global Support Services - filesystems
Red Hat

^ permalink raw reply	[flat|nested] 9+ messages in thread

* [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue
@ 2019-10-26 21:04 Ronnie Sahlberg
  2019-10-27 23:52 ` Frank Sorenson
  0 siblings, 1 reply; 9+ messages in thread
From: Ronnie Sahlberg @ 2019-10-26 21:04 UTC (permalink / raw)
  To: linux-cifs

Steve, Pavel, Frank

This patch moves the logic in cifsFileInfo_put() into a work-queue so that
it will be processed in a different thread which, importantly, does not hold
any other locks.

This should address the deadlock that Frank reported in the thread:
Yet another hang after network disruption or smb restart -- multiple file writers



^ permalink raw reply	[flat|nested] 9+ messages in thread

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Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-29  3:13 [PATCH 0/1] cifs: move cifsFileInfo_put logic into a work-queue Ronnie Sahlberg
2019-10-29  3:13 ` [PATCH] " Ronnie Sahlberg
2019-10-29 23:19   ` Pavel Shilovsky
2019-10-30  1:25     ` ronnie sahlberg
2019-10-30 15:57       ` Pavel Shilovsky
  -- strict thread matches above, loose matches on Subject: below --
2019-10-30  2:59 [PATCH 0/1] " Ronnie Sahlberg
2019-10-26 21:04 Ronnie Sahlberg
2019-10-27 23:52 ` Frank Sorenson
2019-10-28 22:51   ` Pavel Shilovsky

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Example config snippet for mirrors

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