forked from Minki/linux
6ed09c34b7
This patch fixes the following UBIFS assertion warning: UBIFS assert failed in do_readpage at 115 (pid 199) [<b00321b8>] (unwind_backtrace+0x0/0xdc) from [<af025118>] (do_readpage+0x108/0x594 [ubifs]) [<af025118>] (do_readpage+0x108/0x594 [ubifs]) from [<af025764>] (ubifs_write_end+0x1c0/0x2e8 [ubifs]) [<af025764>] (ubifs_write_end+0x1c0/0x2e8 [ubifs]) from [<b00a0164>] (generic_file_buffered_write+0x18c/0x270) [<b00a0164>] (generic_file_buffered_write+0x18c/0x270) from [<b00a08d4>] (__generic_file_aio_write+0x478/0x4c0) [<b00a08d4>] (__generic_file_aio_write+0x478/0x4c0) from [<b00a0984>] (generic_file_aio_write+0x68/0xc8) [<b00a0984>] (generic_file_aio_write+0x68/0xc8) from [<af024a78>] (ubifs_aio_write+0x178/0x1d8 [ubifs]) [<af024a78>] (ubifs_aio_write+0x178/0x1d8 [ubifs]) from [<b00d104c>] (do_sync_write+0xb0/0x100) [<b00d104c>] (do_sync_write+0xb0/0x100) from [<b00d1abc>] (vfs_write+0xac/0x154) [<b00d1abc>] (vfs_write+0xac/0x154) from [<b00d1c10>] (sys_write+0x3c/0x68) [<b00d1c10>] (sys_write+0x3c/0x68) from [<b002d9a0>] (ret_fast_syscall+0x0/0x2c) The 'PG_checked' flag is used to indicate that the page does not supposedly exist on the media (e.g., a hole or a page beyond the inode size), so it requires slightly bigger budget, because we have to account the indexing size increase. And this flag basically tells that the budget for this page has to be "new page budget". The "new page budget" is slightly bigger than the "existing page budget". The 'do_readpage()' function has the following assertion which sometimes is hit: 'ubifs_assert(!PageChecked(page))'. Obviously, the meaning of this assertion is: "I should not be asked to read a page which does not exist on the media". However, in 'ubifs_write_begin()' we have a small "trick". Notice, that VFS may write pages which were not read yet, so the page data were not loaded from the media to the page cache yet. If VFS tells that it is going to change only some part of the page, we obviously have to load it from the media. However, if VFS tells that it is going to change whole page, we do not read it from the media for optimization purposes. However, since we do not read it, we do not know if it exists on the media or not (a hole, etc). So we set the 'PG_checked' flag to this page to force bigger budget, just in case. So 'ubifs_write_begin()' sets 'PG_checked'. Then we are in 'ubifs_write_end()'. And VFS tells us: "hey, for some reasons I changed my mind and did not change whole page". Frankly, I do not know why this happens, but I hit this somehow on an ARM platform. And this is extremely rare. So in this case UBIFS does the following: 1. Cancels allocated budget. 2. Loads the page from the media by calling 'do_readpage()'. 3. Asks VFS to repeat the whole write operation from the very beginning (call '->write_begin() again, etc). And the assertion warning is hit at the step 2 - remember we have the 'PG_checked' set for this page, and 'do_readpage()' does not like this. So this patch fixes the problem by adding step 1.5 and cleaning the 'PG_checked' before calling 'do_readpage()'. All in all, this patch does not fix any functionality issue, but it silences UBIFS false positive warning which may happen in very very rare cases. And while on it, this patch also improves a commentary which explains the reasons of setting the 'PG_checked' flag for the page. The old commentary was a bit difficult to understand. Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com> |
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| .. | ||
| budget.c | ||
| commit.c | ||
| compress.c | ||
| debug.c | ||
| debug.h | ||
| dir.c | ||
| file.c | ||
| find.c | ||
| gc.c | ||
| io.c | ||
| ioctl.c | ||
| journal.c | ||
| Kconfig | ||
| key.h | ||
| log.c | ||
| lprops.c | ||
| lpt_commit.c | ||
| lpt.c | ||
| Makefile | ||
| master.c | ||
| misc.h | ||
| orphan.c | ||
| recovery.c | ||
| replay.c | ||
| sb.c | ||
| scan.c | ||
| shrinker.c | ||
| super.c | ||
| tnc_commit.c | ||
| tnc_misc.c | ||
| tnc.c | ||
| ubifs-media.h | ||
| ubifs.h | ||
| xattr.c | ||