f2fs: fix panic issue in update_sit_entry

When CONFIG_F2FS_CHECK_FS is not enabled, f2fs_bug_on just printing
warning, get_new_segment may get an out-of-bounds segment when there
is no free segments. Then a block is allocated from this invalid
segment, update_sit_entry will access the invalid bitmap address,
cause system panic. Just as below call stack:

f2fs_allocate_data_block get a block address with 0x4000 and
partition size is 64MB

[   13.401997] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[   13.402003] Mem abort info:
[   13.402006]   ESR = 0x96000005
[   13.402009]   EC = 0x25: DABT (current EL), IL = 32 bits
[   13.402015]   SET = 0, FnV = 0
[   13.402018]   EA = 0, S1PTW = 0
[   13.402021]   FSC = 0x05: level 1 translation fault
[   13.402025] Data abort info:
[   13.402027]   ISV = 0, ISS = 0x00000005
[   13.402030]   CM = 0, WnR = 0
[   13.402034] user pgtable: 4k pages, 39-bit VAs, pgdp=00000001066ab000
[   13.402038] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000
[   13.402052] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[   13.489854] pc : update_sit_entry+0x128/0x420
[   13.490497] lr : f2fs_allocate_data_block+0x6b0/0xc2c
[   13.491218] sp : ffffffc00e023440
[   13.501530] Call trace:
[   13.501930]  update_sit_entry+0x128/0x420
[   13.502523]  f2fs_allocate_data_block+0x6b0/0xc2c
[   13.503203]  do_write_page+0xf0/0x1d4
[   13.503752]  f2fs_outplace_write_data+0x68/0xfc
[   13.504408]  f2fs_do_write_data_page+0x3a8/0x65c
[   13.505076]  move_data_page+0x294/0x7a8
[   13.505647]  gc_data_segment+0x4b8/0x800
[   13.506229]  do_garbage_collect+0x354/0x674
[   13.506843]  f2fs_gc+0x280/0x68c
[   13.507340]  f2fs_balance_fs+0x104/0x144
[   13.507921]  f2fs_create+0x310/0x3d8
[   13.508458]  path_openat+0x53c/0xc28
[   13.508997]  do_filp_open+0xbc/0x16c
[   13.509535]  do_sys_openat2+0xa0/0x2a0

So sanity check should be add in update_sit_entry.
Also remove some redundant judgment code.

Signed-off-by: Zhiguo Niu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

fs/f2fs/segment.c

@@ -2394,6 +2394,8 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
 #endif
 
 	segno = GET_SEGNO(sbi, blkaddr);
+	if (segno == NULL_SEGNO)
+		return;
 
 	se = get_seg_entry(sbi, segno);
 	new_vblocks = se->valid_blocks + del;
@@ -3465,8 +3467,7 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 	 * since SSR needs latest valid block information.
 	 */
 	update_sit_entry(sbi, *new_blkaddr, 1);
-	if (GET_SEGNO(sbi, old_blkaddr) != NULL_SEGNO)
-		update_sit_entry(sbi, old_blkaddr, -1);
+	update_sit_entry(sbi, old_blkaddr, -1);
 
 	/*
 	 * If the current segment is full, flush it out and replace it with a